fix: network objects to synchronize scene changes edge cases

[NoelStephensUnity]

The PR assures that:

• If a NetworkObject's GameObject is destroyed before it should have been, this is detected and the scene migration synchronization table is cleaned up.
• When NetworkManager shutsdown the scene migration synchronization table is cleared.

MTTB-1025
MTTB-1027

This PR also removes the static NetworkObjectsToSynchronizeSceneChanges table and migrates this script into NetworkSpawnManager.

fix: #3221, #3218

Changelog

• Fixed: Issue where the scene migration synchronization table was not cleaned up if the GameObject of a NetworkObject is destroyed before it should have been.
• Fixed: Issue where the scene migration synchronization table was not cleaned up upon NetworkManager shutting down.

Testing and Documentation

• Includes integration test updates to NetworkObjectDestroyTests and NetworkSceneManagerEventDataPoolTest.
• No documentation changes or additions were necessary.