Add the new bloom style under a feature flag. (#4033)

* Refactor the bloom into a modifier.

It currently depends on the home screen context but that will be removed in the future.

* Add an initial implementation of the new bloom using an image on the navigation item's appearance.

* Add a feature flag to control the new bloom.

ElementX/Sources/Screens/HomeScreen/HomeScreenModels.swift

@@ -105,6 +105,10 @@ struct HomeScreenViewState: BindableState {
     
     var reportRoomEnabled = false
     
+    // Intentionally not mutable so that we don't have to reset the navigation bar's
+    // appearance whenever the feature flag is toggled (requires a restart).
+    let isNewBloomEnabled: Bool
+    
     var visibleRooms: [HomeScreenRoom] {
         if roomListMode == .skeletons {
             return placeholderRooms