This new navbar component is used for every navbar in chat, full page or drawer, and any screen.
This commit also uses this opportunity to correctly decouple drawer-routes from full page routes. This will avoid having this kind of properties in components: `@includeHeader={{false}}`. The header is now defined in the parent template using a navbar. Each route has now its own template wrapped in a div of the name of the route, eg: `<div class="c-routes-threads">..</div>`.
The navbar API:
```gjs
<Navbar as |navbar|>
<navbar.BackButton />
<navbar.Title @title="Foo" />
<navbar.ChannelTitle @channel={{@channel}} />
<navbar.Actions as |action|>
<action.CloseThreadButton />
</navbar.Actions>
</navbar>
```
The full list of components is listed in `plugins/chat/assets/javascripts/discourse/components/navbar/index.gjs` and `plugins/chat/assets/javascripts/discourse/components/navbar/actions.gjs`.
Visually the header is not changing much, only in drawer mode the background has been removed.
This commit also introduces a `<List />` component to facilitate rendering lists in chat plugin.
- sticky doesn't work well with overflow: hidden parents. These overflows were used to hide other issues which shouldn't exist anyways. If it causes issues we should fix the root cause.
- our `--header-offset` is changing a lot on safari while scrolling, sometimes with very unexpected value like: negative or very high value, which causes the navbar to appear at unexpected positions for few ms, this commit is using the value of the header on insert and not changing it after, it shouldn't cause any issue.
This commit adds a new "My threads" link in sidebar and drawer. This link will open the "/chat/threads" page which contains all threads where the current user is a member. It's ordered by activity (unread and then last message created).
Moreover, the threads list of a channel page is now showing every threads of a channel, and not just the ones where you are a member.
