Avoid errors when dispatching mount operations within mount hooks (#50091)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/50091

Changelog: [internal]

If a library uses mount hooks to perform mount operations, it's possible to get concurrent modifications of the list of pending surface IDs to report.

This fixes that potential error by making a copy of the list before dispatching the mount notifications.

Fixes https://github.com/facebook/react-native/issues/49783.

Reviewed By: javache

Differential Revision: D71387739

fbshipit-source-id: 96c723ef2d6bcc659c4452434b7a4d5af26117ef