fix: Migrate OnClientConnectedCallback invocation into StartHost [MTT-4972]

[NoelStephensUnity]

This assures that any NetworkBehaviour components attached to in-scene placed NetworkObjects will have their associated netcode/NetworkManager properties properly initialized when OnClientConnected is invoked.

MTT-4972

Changelog

• Fixed: The issue where NetworkManager.OnClientConnectedCallback was being invoked before in-scene placed NetworkObjects had been spawned when starting NetworkManager as a host.

Testing and Documentation

• Includes integration test (wip)

[JesseOlmer]

Is there a bug # this is associated with?

HandleConnectionApproval just above in the same method invokes onclientconnected... either directly if scene management is disabled, or at the end of the Synchronize scene event if scene management is enabled.

Isn't this change just going to fire it multiple times?

[NoelStephensUnity]

Is there a bug # this is associated with?

HandleConnectionApproval just above in the same method invokes onclientconnected... either directly if scene management is disabled, or at the end of the Synchronize scene event if scene management is enabled.

Isn't this change just going to fire it multiple times?

Yeah, I forgot to mark it as draft. It was just a quick first pass example of what it would sort of look like. (still needs a ticket)
Whether scene management is enabled or disabled, it will only get invoked in StartHost (clients will only execute that block of code I think you are referring to within HandleConnectionApproved)
It will not get invoked within NetworkSceneManager during a Synchronize scene event as that is only invoked on clients and not on the server-side (server is already synchronized).