GetPlayerNetworkObject should throw exceptions if used wrong

[LukeStampfli]

Is your feature request related to a problem? Please describe.
NetworkSpawnManager.GetPlayerNetworkObject will only work on the server for all clients because clients aren't aware of each other. If I use this as a client for another clients id it will just return null.

Describe the solution you'd like
Add the following lines at the beginning of it:

if !(NetworkManager.Singleton.LocalClientId == clientId){
    throw new NotServerException("Only the server can find player objects from other clients.");
}

Describe alternatives you've considered
In theory the client could be aware of player objects of other clients. Because we always populate owner id and whether an object is a player object over the network. So we could maintain all clients which have at least 1 owned NetworkObject in the NetworkManager.Singleton.ConnectedClients dictionary.

Additional context
Add any other context or screenshots about the feature request here.

[SamuelBellomo]

I ran into this issue as well.
Regarding your alternative, one could argue this could be a security issue to distribute client info to all other clients by default. I'd be down for the "throw an error" route and let users implement their own sharing if they want to (like in boss room for the character select screen)

[SamuelBellomo]

Doc should be corrected as well, since it currently gives the wrong impression this can be called from anywhere