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 rev. adds params to the 'web_read_group' method, allowing to
search_read records inside each groups in a single RPC, instead of
doing a 'web_read_group' RPC followed by n 'search_read' RPCs,
where n is the number of opened groups.

Part of task 1915702

With this rev., when there are a lot of groups in a grouped list
view, groups are displayed under several pages, whereas they were
all displayed in the same page before.

This is especially interesting with the new 'expand' attribute, to
ensure that we don't read records for a large number of groups.

By default, the groups limit is set to 80 (like records), and to 10
is the 'expand' attribute is set to true. This limit can be
overriden with the 'groups_limit' attribute.

Part of task 1915702

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 this commit, some breaking spaces were present in the js code.
Such spaces are misinterpreted and worked by luck.

This has become a problem with exported js bunldes (e.g. the
external_lib bundle in im_livechat).

This commit replaces breaking spaces by regular spaces.

Example of failing request:
```
rpc.query({
    model: 'link.tracker.click',
    method: 'read_group',
    args: [[links_domain, ['create_date', '>', interval]], ['country_id']],
    kwargs: {groupby:'country_id'},
});
```

The RPC request built contains the following:
```
args: [[["link_id", "=", 1]], ["create_date"]]
kwargs: {groupby: "create_date:day", domain: [], fields: []}
```

This will be interpreted server side as:
```
model.read_group([['link_id', '=', 1]], ['create_date'], groupby=['create_date:day'], domain=[], fields=[])
```

2 arguments match `domain` and `fields`, which causes a crash.

opw-781300

The previous code used to create its own args array
for the search_read method, replacing the one that
was originally given to it.

This lead to silent errors since positional arguments
to this function were completely ignored in the case
of search_read.

I took this commit as an opportunity to improve a
bit on the current state of these rpc helpers.
Namely, the basic args/kwargs priority is the following (top-to-bottom):
- kwargs defined in the rpc call
- kwargs defined in the kwargs key of the params kwarg of the rpc call
- positional arguments are passed as is

For read_group and search_read methods, the priority is the following:
- kwargs defined in the rpc call
- kwargs defined in the params kwarg to the rpc call
- kwargs defined in the kwargs key of the params kwarg of the rpc call
- positional arguments are passed as is

For the /web/dataset/search_read controller, only the params kwarg is
supported, resulting in the following priority:
- kwargs defined in the rpc call
- kwargs defined in the params kwarg to the rpc call
- positional arguments are passed as is

If both a kwargs and a positional arg is given for the same parameter,
it will be sent as is to the server which will crash with a typical
"got multiple values for keyword argument" TypeError. However, in the
MockServer however, we give priority to kwargs over args in this case.

Please note that I also chose to remove unnecessary default values so
that the ones actually used are the ones from the server, not the ones
that were duplicating those in the rpc js file.

The lazy option in read_group is by default true, so when we want to
override it with false, it needs some special care.

The RPC system was not completely satisfactory, we decided to prepare
the future and do it properly.  This commit introduces the new rpc
system, which replace the previous new one.  We now simply have a
method, this._rpc, which takes a dictionary of parameters.  The idea is
that depending on the parameters, it is able to add correct default
value when necessary.

For situations where we don't have the this._rpc method, we can use the
rpc.query method, which takes the same arguments, but directly calls
ajax.rpc instead of triggering up some events.

This rev. allows to specify some kwargs of read_group directly in
an Object given to kwargs(), instead of explicitly specify them
using the corresponding method (e.g. to specify the context in the
kwargs instead of by calling .withContext().