Launch app on dedicated GPU on NVIDIA Prime

Was added to GNOME 3.36. I'm not sure how exactly this works, but it sounds like NVIDIA GPU would not be used for most things, but you could choose to launch an app (i.e. a game or video editor) using the GPU.

We should see how it looks and is implemented under-the-hood in GNOME, as well as how it looks on macOS (which I _believe_ has a similar feature on its discrete GPU models). If the heavy lifting is done by Mutter or other upstream components, it would be a nice feature.

This would likely require updates to Plank and Applications Menu to add an item into app launchers' context menus.