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/Application/AppSettings.swift

@@ -48,6 +48,7 @@ final class AppSettings {
         case hideUnreadMessagesBadge
         case hideInviteAvatars
         case timelineMediaVisibility
+        case isNewBloomEnabled
         
         case elementCallBaseURLOverride
         
@@ -361,6 +362,9 @@ final class AppSettings {
     
     @UserPreference(key: UserDefaultsKeys.timelineMediaVisibility, defaultValue: TimelineMediaVisibility.always, storageType: .userDefaults(store))
     var timelineMediaVisibility
+    
+    @UserPreference(key: UserDefaultsKeys.isNewBloomEnabled, defaultValue: false, storageType: .userDefaults(store))
+    var isNewBloomEnabled
 }
 
 extension AppSettings: CommonSettingsProtocol { }