Extract composer toolbar to a dedicated component (#1427)

* Extract composer toolbar to a dedicated component

* Use publisher for composer mode

* Introduce `RoomScreenComposerProvider`

* Add `ComposerToolbarViewModelTests`

* Rename protocols and add passthrough subjects for focused and composer mode

* Remove `ComposerToolbarViewActionHandler` and `ComposerToolbarCoordinatorParameters`

* Remove `RoomScreenComposerActionHandlerProtocol` and `RoomScreenComposerProviderProtocol`

* Re-arrange code a bit

* Remove composer mode being stored on `RoomScreen`

* Rename `process(viewAction: ComposerToolbarViewAction)` to `process(composerAction: ComposerToolbarViewAction)`

* Replace PassthroughSubject with direct function call

* Remove `ComposerToolbarCoordinator`

* Remove `cancelEdit` and `cancelReply` from external composer view model actions

* Use `RoomScreenComposerAction` as a sub-`RoomScreenViewModelAction`

* Move `ComposerToolbarViewModel` callback to actionsSubject

* Move `RoomScreenViewModel` callback to actionsSubject

* Fix `RoomScreenViewModelTests`

* Rename `composerAction` parameter to `roomAction`

* Fix unit tests

ElementX.xcodeproj/project.xcworkspace/xcshareddata/swiftpm/Package.resolved

@@ -208,7 +208,7 @@
     {
       "identity" : "swiftui-introspect",
       "kind" : "remoteSourceControl",
-      "location" : "https://github.com/siteline/SwiftUI-Introspect",
+      "location" : "https://github.com/siteline/SwiftUI-Introspect.git",
       "state" : {
         "revision" : "b94da693e57eaf79d16464b8b7c90d09cba4e290",
         "version" : "0.9.2"