add gamepad support

[Trial97]

fixes #791 no idea how to fix the CI but the code works for local :)

[Trial97]

Status update:

• nix fails because it doesn't pull the submodules
• and all other stuff fails because it can't find the SDL2 header files

[Lutitious]

testing on windows with an xbox controller, the mouse is very jittery and behaves as a dpad even though it is being controlled by the analogue stick. Any launched window or menu causes the mouse to become unresponsive and the dpad selection also no longer works.

[Trial97]

Thinking about closing this in favor of other external tools that add this.

[ttang4299]

@Trial97 That's fair. Would it be built into the launcher? Just wondering if it would be streamlined for ease of use with Steam Deck users.

[Trial97]

@ttang4299 see https://github.com/PrismLauncher/PrismLauncher/issues/791#issuecomment-2143720678 But no I don't think there will be an integration with the launcher.