Use native video call picture in picture! (#3190)

* Use native video call picture in picture!

* Handle isSupported, isPossible and web view errors.

* Use new canEnterPip method.

* Hide a room's Call button when already joined to the call.

* Tweak feature flag description.

* PR comments.

ElementX/Sources/Application/AppSettings.swift

@@ -47,6 +47,7 @@ final class AppSettings {
         case publicSearchEnabled
         case fuzzyRoomListSearchEnabled
         case pinningEnabled
+        case elementCallPictureInPictureEnabled
     }
     
     private static var suiteName: String = InfoPlistReader.main.appGroupIdentifier
@@ -285,8 +286,8 @@ final class AppSettings {
     @UserPreference(key: UserDefaultsKeys.pinningEnabled, defaultValue: false, storageType: .userDefaults(store))
     var pinningEnabled
     
-    // Not user configurable as it depends on work in EC too.
-    let elementCallPictureInPictureEnabled = false
+    @UserPreference(key: UserDefaultsKeys.elementCallPictureInPictureEnabled, defaultValue: false, storageType: .userDefaults(store))
+    var elementCallPictureInPictureEnabled
         
     #endif