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.

---------

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

tests/konsist/src/test/kotlin/io/element/android/tests/konsist/KonsistArchitectureTest.kt

@@ -35,6 +35,7 @@ class KonsistArchitectureTest {
             .withNameEndingWith("State")
             .withoutName(
                 "CameraPositionState",
+                "CustomSheetState",
             )
             .constructors
             .parameters

tests/uitests/src/test/snapshots/images/ui_S_t[f.messages.impl.mentions_null_MentionSuggestionsPickerView_-D-3_3_null,NEXUS_5,1.0,en].png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
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+size 18686

tests/uitests/src/test/snapshots/images/ui_S_t[f.messages.impl.mentions_null_MentionSuggestionsPickerView_-N-3_4_null,NEXUS_5,1.0,en].png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:0e52de245ef2c4a423849ab0ff592109e51c2c25e0cbc1335812a37986c27b06
+size 18411