Mark PlayerCanRestart in GameMode as BlueprintCallable

Because the built-in PC’s ServerRestartPlayer logic only works if a PC is ‘inactive’, which for clients that simply unpossessed a Pawn during gameplay are treated as ‘Playing’, there is no built-in path for clients to trigger a server respawn request that respects GameMode’s PlayerCanRestart logic using Blueprints.

Allowing Blueprints to call PlayerCanRestart can at least give Blueprints the ability to respect GameMode logic when creating a custom respawn setup.