[iOS][ContextMenus] Fixes ContentSuggestions preview

This CL fixes the dismissal animation of most visited tiles.
Most Visited tile appears blank for a moment switching from incognito to
normal tab after opening the link in a new incognito tab from context
menu because there was no preview configured.
To fix this, the view of the ContentSuggestionsViewController is used as
a preview.

see: https://drive.google.com/drive/folders/1EZFa-TvlJRsqVp6mwMBz0H7e6EZL0c7e?usp=sharing

Bug: 1117487
Change-Id: I1d80592e566c92cdd3b9846e74a4af53d697ee47
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2526086Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Ewann Pellé <ewannpv@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825349}

ios/chrome/browser/ui/content_suggestions/content_suggestions_view_controller.mm

@@ -495,6 +495,14 @@ NSString* const kContentSuggestionsMostVisitedAccessibilityIdentifierPrefix =
   return cell;
 }
 
+- (UITargetedPreview*)collectionView:(UICollectionView*)collectionView
+    previewForDismissingContextMenuWithConfiguration:
+        (UIContextMenuConfiguration*)configuration API_AVAILABLE(ios(13.0)) {
+  UITargetedPreview* preview =
+      [[UITargetedPreview alloc] initWithView:self.view];
+  return preview;
+}
+
 - (UIContextMenuConfiguration*)collectionView:(UICollectionView*)collectionView
     contextMenuConfigurationForItemAtIndexPath:(NSIndexPath*)indexPath
                                          point:(CGPoint)point