GlobalObjectIdHash collisions occur when a prefab has instances in multiple scenes before adding NetworkObject

[zachstronaut]

Description

When a prefab exists in multiple scenes, and then later you add a NetworkObject that that prefab, the instances will have GlobalObjectIdHash collisions in any unopened scenes when you make this edit.

Reproduce Steps

1. Open Bossroom sample
2. Open DungeonEntrance scene
3. Create a new prefab and add two instances to scene and save
4. Open DungeonBossRoom scene
5. Add two instances of the new prefab to scene and save
6. Edit the prefab and add a NetworkObject
7. Open Startup scene
8. Run game and ready-up into gameplay
9. Error will occur

Actual Outcome

"Exception: TestPrefab (1) tried to registered with ScenePlacedObjects which already contains the same GlobalObjectIdHash value 3700887716 for TestPrefab!"

Expected Outcome

Every instance of the prefab would have a unique id.

Netcode needs a way to handle NetworkObject GUIDs (GlobalObjectId) outside of OnValidate() because of issues like this. Netcode also doesn't provide any menu option to re-issue ids to every NetworkObject in a scene and we've had to build that ourselves.

Environment

• OS: Windows 11
• Unity Version: 2022.3.0, 2021.3.11
• Netcode Version: 1.4.0, 1.5.1

[zachstronaut]

Additionally, if you open the scenes after the fact and look at these new NetworkObjects in the Inspector they will visually show unique ids but the scene will not be dirty so it will not be save-able.

[NoelStephensUnity]

@zachstronaut
I believe #2662 resolves this issue.
Did a quick test using some of the test project scenes and it seemed to work fine.
(will run the exact same steps you outlined above using Boss Room in the morning to double check)