Add descriptive window titles when using debug/run_multuple_instances

[kit-solent]

When using debug/run_multuple_instances I find it hard to know which window is which debug session. I am making an online multiplayer game and my separate windows are giving different error messages but I don't know which errors are associated with the host and which with the client.

If the window title was changed from <Game Name> (DEBUG) to <Game Name> (DEBUG session 1) then it would be easier to correctly interpret error messages.

[Calinou]

• This is already being tracked in Identify instance windows when using launching multiple instances #3357.