Refactor Knowledge to use the new features of the editor. Behaviors are
converted to Embedded Components which are now natively supported in the
html_editor module. (Embedded Components is a feature of the HtmlField allowing
to mount Owl components inside an HtmlField value, based on metadata stored in
the attributes of html nodes)

### website_knowledge is no longer forgotten

Public version of an article is now using the HtmlViewer to render the Html
value, and this allows to mount embedded components as they would be in the
backend view. This results in a far better reading experience for public users.

### Comments

Overhaul of the feature, in a concise way: anchoring a comment in the HtmlField
value is way less expensive in terms of amount of characters since it uses 2
self closing `<a>` nodes instead of wrapping every text node in a `<span>`
(which could be hundreds for a comment spanning over an entire document). This
is also easier to manage during edition, since new nodes between the boundaries
of a comment don't need to be processed so that they are marked as part of a
comment anymore.

Loading threads and messages is now centralized in a `comments_service` which
batches rpc calls together, significantly reducing the load when opening an
article.

The comment panel now has a "load more" feature, meaning that it does not load
every single existing thread and their messages at once when opening it.

Floating "Comment boxes" are now perfectly aligned with their anchor in the
HtmlField when they are focused (previously they were pushed by other Comments
boxes above them when there was not enough space, even when active).

### Embedded Components

All existing Behaviors are converted to embedded components, and some of them
are moved in the html_editor module

#### knowledge:
- Article Link
- Article Index
- Clipboard
- Embedded View
- Embedded view Link
#### html_editor:
- Excalidraw
- File
- Table of Content
- Video

### Migration

Since metadata for Behaviors differ from those of Embedded Components, and
upgrading an html value is expensive, this transition will be handled
client-side for starts. A small JS upgrade feature for html values is
introduced. The "upgrade" will be attempted once, and won't result in a crash if
it fails. Instead, the previous value will be conserved, and the user will be
able to adjust the content manually by using editor commands.

Odoo Community: https://github.com/odoo/odoo/pull/173997

task-3672747

Co-authored-by: Damien Abeloos <abd@odoo.com>
Co-authored-by: Adrien Schoffeniels <adsc@odoo.com>
Co-authored-by: Julien Banken <jbn@odoo.com>
Co-authored-by: Thomas Josse <thjo@odoo.com>