fix(testing): add TestHint for LargeVideo

Since the main conference container is no longer "clickable" there must
be a way for clicking on the "large video". A clickable TestHint nested
in ParticipantView makes it easier for dealing with the fact that the
click handler is not always on the same component (required for the
pinch and zoom feature to work correctly).

react/features/conference/components/Conference.native.js

@@ -188,10 +188,7 @@ class Conference extends Component<Props> {
      */
     render() {
         return (
-            <Container
-                accessibilityLabel = 'Conference'
-                accessible = { false }
-                style = { styles.conference }>
+            <Container style = { styles.conference }>
                 <StatusBar
                     barStyle = 'light-content'
                     hidden = { true }