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>

This commit adapts tests following recent changes on the helpers.
The main change is that addMockEnvironment (and all functions using
it) are now async, as they need to wait for services to be started.

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>

This rev. introduces robust helpers to use in the JS tests suite to
interact with DOM and components, and starts using them (almost)
everywhere.

All the helpers are exposed though testUtils.js.

There are 2 kinds of helpers:

1. Assertions
-------------
 * assert.containsNone, containsN, containsOnce check that the DOM
   (or a specific part of the DOM) contains a `selector`. It
   generates a correct error message automatically.
    ex: assert.strictEqual(form.$('.o_form_editable'), 1, "msg");
        -> assert.containsOnce(form, '.o_form_editable');
 * assert.isVisible, isNotVisible check that the DOM has an element
   visible or not. They also check that the element is actually in
   the DOM (before most tests didn't verify this).
 * assert.hasClass, doesNotHaveClass, hasAttrVAlue, check specific
   properties of a DOM element, and also validate that it is
   applied on a single existing DOM element (before most tests
   didn't verify this).
    ex: assert.notOk(form.$('button').hasClass('btn-primary'));
       -> assert.doesNotHaveClass(form.$('button'), 'btn-primary');

2. Utilities
------------
The goal of the utilities is to centralize the definition of many
standard components and interactions, ensuring that when we
refactor the JS framework, we do not need to change all the tests.

Existing mock utilities (addMockEnvironment, intercept, path,
patchDate, unpatch and fieldsViewGet) are moved to
'testUtils.mock.*'.
Existing DOM utilities are moved to 'testUtils.dom.*'.
New dom utilities are created for opendDatePicker, click,
clickFirst and clickLast. Helper `click` verifies that there is
exactly 1 element visible in the DOM you click on, `clickFirst`
and `clickLast` verify that there are more than one element on the
DOM.
 ex: form.$('button').click();
     -> testUtils.dom.click(form.$('button'));

New Form utilities: (testUtils.form.*)
 clickEdit, clickSave, clickCreate, clickDiscard, all clicks on
 the control panel buttons of the form.
 `reload` reloads the form data.

New modal, graph, kanban and pivot utils (testUtils.pivot.*,
testUtils.kanban.*, etc.).

New fields utils: (testUtils.fields.*)
 * editInput, editSelect: allow to change the value of a field,
   using a selector to identify it. They validate that the input
   exists and trigger the change event automatically.
 * editAndTrigger: allow to modify a field and trigger specific
   events after the value change
 * many2one (testUtils.fields.many2one.*)
   clickOpenDropdown, clickHighlightedItem, clickItem,
   searchAndClickItem: use a field name instead of a selector and
   do all the complex mechanism to open, filter and highlight
   many2one fields.

Joint work with aab, dam, ged, mge, svs and vsc.

Before this commit, DMs had the prefix '#' in their
displayed name (e.g. '#Demo User').

This commit fixes the issue by putting this prefix
only on non-chat DMs. In particular, mailboxes, DMs
and Livechats no longer show this prefix. This change
is also visible in the breadcrumb of the discuss app.

Task-ID 1911738

This commit fixes some bugs on thread windows, and make some
improvements on tests related to thread windows.

Fixes:

	1. Correctly position last visible thread window when there are more
	   open thread windows than available slots.
	2. Closing a thread window now marks it as read.
	3. Can now fold/unfold the blank thread window (aka 'New' thread window).

Tests cleaning:

	1. Removed unnecessary 'before assertions' in thread window tests.
	   > Solved with this: https://github.com/odoo/odoo/commit/9b1daa1218f7adf9d741afba607ef5b55b16e3e6
	1. Added basic rendering test for a (non-blank) thread window.
	2. Cleaned thread window tests
	   > Split in different files.
	   > Grouped in 'Thread Window' QUnit module.