Initial support for member suggestions (#1631)

* Initial support for member suggestion (search and UI)

* Add custom `BottomSheetScaffold` implementation to workaround several scrolling bugs

* Start searching as soon as `@` is typed, add UI following initial designs

* Extract suggestion processing code

* Extract component, add previews, fix tests

* Add tests

* Add exception from kover to the forked bottom sheet code

* Add a feature flag for mentions

- Extract composer & mention suggestions to their composable.
- Extract mentions suggestions processing to its own class.
- Add `MatrixRoom.canTriggerRoomNotification` function.
- Update strings and conditions for displaying the `@room` mention.

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Co-authored-by: ElementBot <benoitm+elementbot@element.io>

tools/localazy/config.json

@@ -112,6 +112,7 @@
       "name": ":features:messages:impl",
       "includeRegex": [
         "screen_room_.*",
+        "screen\\.room\\..*",
         "screen_dm_details_.*",
         "room_timeline_state_changes"
       ],