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>

build.gradle.kts

@@ -200,7 +200,9 @@ koverMerged {
                     "*Node$*",
                     // Exclude `:libraries:matrix:impl` module, it contains only wrappers to access the Rust Matrix SDK api, so it is not really relevant to unit test it: there is no logic to test.
                     "io.element.android.libraries.matrix.impl.*",
-                    "*Presenter\$present\$*"
+                    "*Presenter\$present\$*",
+                    // Forked from compose
+                    "io.element.android.libraries.designsystem.theme.components.bottomsheet.*",
                 )
             )
         }