[Feature request] Show gs_frame while loading savestates

[Megamouse]

Currently the savestates are loaded first in a blocking fashion and then we init the fxos, passing the archive to the GsRender.
This means the user will not have any feedback whatsoever when booting a savestate until the game window finally pops up.

Therefore we should:

• Detach the rsx_thread init from the window and overlay init
• Show the game window immediately with either a simple overlay or the current progress of loading the savestate.
• Enjoy the loading screen