fix: GlobalObjectidHash serializing invalid values [MTT-77098]

[NoelStephensUnity]

This PR resolves several issues with the generation of the GlobalObjectIdHash value:

• When editing a prefab, it was possible that an invalid GlobalObjectIdHash value could be serialized.
  • This invalid value could "hide itself" as viewing the prefab asset in the inspector view, when no longer editing the prefab, would show a valid value but the previous invalid serialized value would still be applied in playmode and/or runtime builds.
    • A work around would be to revalidate each (network) prefab that this could have happened to.
• When creating a prefab from an in-scene placed object, the current recommended next action would be to delete the original in-scene placed object and create a new instance of that object from the newly created prefab.
  • This extra step was a work around for an issue directly related to how the prefab was being generated and updated.
• Depending upon the scenario, it was possible for a GlobalObjectIdHash value to be updated but the asset not marked as being dirty.
  • This could impact multi-editor based sessions (MPPM, Parrel Sync, etc.) where instances would not be updated to the changed GlobalObjectIdHash value.
  • This was also a part of the issue related to the above described issues.

MTT-7098
fix: #2653
fix: #1499
fix: #2664

Changelog

• Fixed: Issue where generation of the DefaultNetworkPrefabs asset was not enabled by default.
• Fixed: Issue where the GlobalObjectIdHash value could be updated but the asset not marked as dirty.
• Fixed: Issue where the GlobalObjectIdHash value of a (network) prefab asset could be assigned an incorrect value when editing the prefab in a temporary scene.
• Fixed: Issue where the GlobalObjectIdHash value generated after creating a (network) prefab from an object constructed within the scene would not be the correct final value in a stand alone build.

Testing and Documentation

• Created internal manual test project for validation.
• Updated the "Creating In-Scene Placed Network Prefab Instances" section (i.e. it is no longer required to delete the original scene object that the prefab was created from) in PR-1102