This commit is a significant rewriting of client-side discuss, chatter,
chat window, and messaging menu using OWL. The behavior should be broadly
the same, with some slight functional changes here and there.

From a technical standpoint, the code of messaging is mainly organized in 2
main groups of modules:

- models, which are logical entities that depict the client-side state of
  messaging as a whole.
- components, which are in charge of displaying information from models.

This refactoring also introduces new JS guidelines regarding folder structure
(/static) and naming rules for JS modules.

Community PR: https://github.com/odoo/odoo/pull/39023
Enterprise PR: https://github.com/odoo/enterprise/pull/6249

Task-1914207

This PR is a collaborative work by Alexandre, Julien, Sébastien and Xavier,
with the precious help of Lucas to speed it up towards the end.

closes odoo/odoo#39023

Related: odoo/enterprise#6249
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>
Co-authored-by: Alexandre Kühn <aku@odoo.com>
Co-authored-by: Julien Giannone <jgi@odoo.com>
Co-authored-by: Lucas Perais <lpe@odoo.com>
Co-authored-by: Sébastien Theys <seb@odoo.com>
Co-authored-by: Xavier Dubuc <xdu@odoo.com>

Part of task 1896658

Co-authored-by: Aaron Bohy <aab@odoo.com>
Co-authored-by: Christophe Matthieu <chm@odoo.com>
Co-authored-by: Mathieu Duckerts-Antoine <dam@odoo.com>
Co-authored-by: David Monjoie <dmo@odoo.com>
Co-authored-by: Martin Geubelle <mge@odoo.com>
Co-authored-by: svs-odoo <svs@odoo.com>
Co-authored-by: Vincent Schippefilt <vsc@odoo.com>

Before, if the visitor was logged in, anonymous name = user.name.
But if we use anonymous name field even if visitor is not anonymous,
we cannot know, in stat e.g., if the session was really made with
an anonymous visitor or not as the field is always filled in.

Now, if the visitor is not anonymous, we use directly the user.name
but we do not fill in the anonymous name. So that if anonymous name
is null, we know afterwards that the session was made we a real
anonymous visitor.

Since the anonymous name is empty if visitor is logged in,
we cannot use anonymous_name anymore to get the title of the session window.

Task ID : 1895998
Closes PR #28283

Revision on https://github.com/odoo/odoo/commit/cd34f6de727d5b3858420cff3c9d3c5995c4e75c

Resulting of the mail JS refactoring, the list of prefetched suggestions
has been changed as follow:

- before: list of list of mention suggestions `{Array<Object[]>}`
- after: list of mention suggestions `{Object[]}`

The change resulted in wrongly thinking that wrapping the list of
suggestions in a list was pointless, thus simplifying it as a simple
list of mention suggestions.

However, because of this change, it has become much harder to
mention employees and followers of documents from the chatter:
it now always fetches all partner suggestions at all time, whereas
before it was suggesting followers, then employees, and finally all
partners based on the input of the user.

In fact, there was a purpose of using a list of list of prefetched
mention suggestions, which is to group suggestions by "priority":
followers first, then employees, and all partners as a last resort.

This commit re-introduces prefetched mention suggestions as a list
of list of partners, so that it re-becomes easier to mention
followers and partners of a document from the chatter.

Task-ID 1910111

With this commit, most threads show an indicator when a member is typing
something. e.g.

	"Mitchell Stephens is typing..."

Supported threads:

	- DM
	- (public & private) channels
	- Livechat (Website & Backend)

Unsupported threads:

	- mailboxes (e.g. 'Inbox')
	- document thread (= 'Chatter')
	- support channel (with `im_support` module)

Some technical details:

	- This is a mix between 'start'/'stop' and 'regular notify' strategies.
	- On typing text in composer: notify 'start typing' to all members of
	  thread.
	- On clearing text in composer: notify 'stop typing' to all members of
	  thread.
	- A member can only notify once every 2.5 seconds to the server when he
	  starts or stops typing something (throttled, buffered notify call).
	- On receiving a message from someone that is typing: determine that he is
	  no longer typing.
	- On non-empty and unchanged composer text for 5.0 seconds: automatically
	  notifies all members of thread that he is no longer typing anything.
	  (This is like a 'soft / cooperative sender' timeout).
	- On non-receiving a typing notification of someone after 60 seconds:
	  determine that he is not longer typing something (This is like a
	  'hard / receiver assumption' timeout).
	- When some types for more than 50 seconds straight: notify that he is
	  still typing something (again and again every 50 seconds).
	- When two or more people are typing something (Multi-User channels), it
	  displays at most 2 typing users (ordering rule: longer typers first):

	  	"Mitchell Stephens, Marc Brown and more are typing..."

	- Timing summary:

		- Usually 2.5 seconds uncertainty.
    	- Up to 5.0 seconds uncertainty on typer inactivity.
    	- Up to 60 seconds uncertainty on typer page reload / browser tab
    	  closed / etc.

Future Improvements:

	- Detect page reload or browser tab close with loose of longpolling
	  connection

Task-ID 28188

This commit makes a lot of small improvements of the JS of mail and
related modules.

	A. Mail Manager
	---------------

		im_support:

		- [REF] Slightly more robust way to determine a support
		        message, so that it more reliably falls back on
		        default kind of message (i.e. support channel UUID
		        should be clearly set).

		mail:

		- [REF] Improved method names for readability purposes.
		        Some examples:

		        - `fetchFromServer` becomes `fetchMailStateFromServer`
		        - `_initialize{*}` becomes `_update{*}FromServer`
		        - `_isModerator` becomes `_isMyselfModerator`

		- [REF] Use 'template' pattern design to make Include on
				Mail Manager much more robust. In particular,
				the flow is always as follow:

					1. Initialize internal state.
					2. Listen on buses.
					3. Fetch mail data from server.

		- [REF] Improved workflow for thread window workflow
		        (Shorter & more readable).

	B. Mail Tests
	-------------

		- [REF] Thread Window Tests crashes with clean message when
		        there are some thread windows open before running the
		        tests.

	C. (Model) Message
	------------------

		- [REF] Improved method names for readability purposes
				(e.g. `isAuthor` becomes `isMyselfAuthor`).

	D. (Model) Thread
	-----------------

		- [REF] Improved `init` parameters on each kind of thread.
		- [REF] 'Thread With Cache' has been renamed to 'Searchable
		        Thread': it embraces all kinds of threads that can
		        be used with the search view.
		- [REF] 'DM' has been renamed to 'DM Chat' (for clarity).
		- [IMP] New Livechat model in the backend.
		- [REF] No more direct instances of the Channel class: public
		        and private channels are now 'Multi-User' channels,
		        while DM Chat and Livechat are 'Two-User' channels:

		        This change has been made so that instances of classes
		        always have direct classes as "leaf" in the Class
		        modeling. It eases making changes to a certain model
		        without being too constrained by another model.

		- [REF] As a consequence of above changed, the method `isChat`
		        has been renamed to `isTwoUserThread`.

		        This is to avoid confusion with the terminology
		        'chat', which is more like a shortcut for 'quick real-
		        time conversation'. In other words, the property of
		        'chat' depends of the way to interact on a thread, not
		        of the intrinsic type of the thread.

		        Still, some parts have kept the terminology 'chat',
		        such as in the systray messagin menu.

		- [IMP] Added `message_added` and `message_posted` hooks,
		        which may be useful to easily hook on those events.

	E. Thread Widget
	----------------

		- [REF] Now uses a `mail.model.AbstractThread` for the
		        rendering of a thread, instead of a list of
		        `{mail.model.AbstractMessage}`.
		- [FIX] Stick thread scroll height to bottom on new rendering,
		        if it was previously at the bottom of the thread.
		- [REF] Option ORDER has its meaning changed: it now refers
		        to the chronological order of messages in the thread,
		        in which DESC means 'from top to bottom', while ASC
		        means 'from bottom to top'.
		- [REF] Improved doc on templates, in particular with the
	            option `ORDER`.

	F. Thread Window
	----------------

		- [REF] Moved more logic to thread windows, which were
		        previously in Mail Window Manager.
		- [REF] Now hides the thread widget attribute. So instead of
		        `threadWindow.threadWidget.isAtBottom()`, it uses
		        `threadWindow.isAtBottom()`.
		- [FIX] New received messages when not having focus on Odoo
		        tab should always make the corresponding thread
		        windows "passive" (i.e. windows that keep threads
		        unread until click on them).
		- [FIX] Blank thread window (i.e. 'New message' TW) correctly
		        opens Discuss with 'Inbox' when clicking on 'Expand'
		        Button in the title
		- [FIX] Do not display the composer for channels with property
		        'mass-mailing' set in thread windows.

	G. (Website) Livechat
	---------------------

		- [REF] Some `trigger` have been turned into `trigger_up`.
		- [REF] Some logic has been moved to models (e.g.
		        `{im_livechat.model.WebsiteLivechat}`), from
		        `{im_livechat.im_livechat.LivechatButton}`.
		- [FIX] New messages should be received in real-time. The
		        longpolling was broken with a recent refactoring on
		        bus service (6448420c5dd160470e465dee7729d19d8d5e7bab).