faf-linux Switch to the Steam Runtime

Most recent problems appear to be caused by unpredictable host environments. Subtle differences between distributions result in issues that take disproportionately long to debug. Wine is not exactly good at printing useful error messages, and Proton patches are even worse in that regard. Something as simple as a missing library on the host will manifest as some absurd problem like the cursor mapping to the wrong part of the screen.

Valve has already fixed this class of issues with the Steam Linux Runtime. Steam launches games configured for Proton Experimental in Steam Runtime 3 ("sniper") using pressure-vessel, which sets up a stable environment for the game using containers and additionally deals with graphics drivers if necessary (cough Nvidia). Switching to the Steam Runtime allows us to reuse existing infrastructure and should vastly reduce the amount of non-reproducible issues in the future.

Why not just ship prebuilt Wine like Lutris does?

Proton's build of Wine has generally worked better for running FA
Proton Wine has fshack, which makes initial setup less of a headache since FA can't autodetect the screen resolution
Most people use Steam and thus have Proton and the Steam Runtime installed already, which reduces the need to download more things
Proprietary software is not a concern since Proton and the Steam Runtime are open source, even if the main Steam client is not. Additionally, FA is already proprietary.
Shipping prebuilt Wine without a container does not fix library compatibility issues. Shipping a container is possible, but is yet more work that Valve/Collabora have quite frankly already done and open-sourced.