fix(rn,filmstrip) avoid fast scroll trigggering visibility notifications

An item won't be considered visible until it has been visible for 500ms.

react/features/filmstrip/components/native/Filmstrip.js

@@ -95,8 +95,10 @@ class Filmstrip extends PureComponent<Props> {
         this._separateLocalThumbnail = Platform.OS !== 'android';
 
         this._viewabilityConfig = {
-            itemVisiblePercentThreshold: 30
+            itemVisiblePercentThreshold: 30,
+            minimumViewTime: 500
         };
+
         this._keyExtractor = this._keyExtractor.bind(this);
         this._getItemLayout = this._getItemLayout.bind(this);
         this._onViewableItemsChanged = this._onViewableItemsChanged.bind(this);

react/features/filmstrip/components/native/TileView.js

@@ -111,8 +111,10 @@ class TileView extends PureComponent<Props> {
         this._keyExtractor = this._keyExtractor.bind(this);
         this._onViewableItemsChanged = this._onViewableItemsChanged.bind(this);
         this._renderThumbnail = this._renderThumbnail.bind(this);
+
         this._viewabilityConfig = {
-            itemVisiblePercentThreshold: 30
+            itemVisiblePercentThreshold: 30,
+            minimumViewTime: 500
         };
         this._flatListStyles = {
             ...styles.flatListTileView