[fabric] Disable view flattening for views using mouse events

Summary:
Views having mouse event handlers assigned to them should not be flattened so that the mouse tracking for the area they cover would work at all times.

This diff disabled view flattening if either of the mouse event handlers is set.

Test Plan: Tested later in this stack.

Reviewers: shawndempsey, #rn-desktop

Reviewed By: shawndempsey

Differential Revision: https://phabricator.intern.facebook.com/D53529017

Tasks: T154617556

Author: Nick Lefever

packages/react-native/ReactCommon/react/renderer/components/view/platform/macos/react/renderer/components/view/HostPlatformViewTraitsInitializer.h

@@ -17,7 +17,9 @@ inline bool formsStackingContext(const ViewProps& props) {
 }
 
 inline bool formsView(const ViewProps& props) {
-  return props.focusable;
+  return props.focusable ||
+         props.macOSViewEvents[MacOSViewEvents::Offset::MouseEnter] ||
+         props.macOSViewEvents[MacOSViewEvents::Offset::MouseLeave];
 }
 
 } // namespace facebook::react::HostPlatformViewTraitsInitializer