Do not flatten view if prop accessibilityViewIsModal is true

Summary:
changelog: [internal]

As per title, prevent view from flattening if `accessibilityViewIsModal` is true.

Reviewed By: jimmy623

Differential Revision: D30696223

fbshipit-source-id: 0c6bfc116458d1808f152cb13ba6c941c58f052e

Author: sammy-SC

ReactCommon/react/renderer/components/view/ViewShadowNode.cpp

@@ -42,6 +42,7 @@ void ViewShadowNode::initialize() noexcept {
       viewProps.getClipsContentToBounds() ||
       isColorMeaningful(viewProps.shadowColor) ||
       viewProps.accessibilityElementsHidden ||
+      viewProps.accessibilityViewIsModal ||
       viewProps.importantForAccessibility != ImportantForAccessibility::Auto ||
       viewProps.removeClippedSubviews;