Game Menu: Replace vkBasalt checkbox with generic Vulkan Post Processing dropdown

[sonic2kk]

Replaces the "Use vkBasalt" checkbox on the Game Menu with a dropdown which can contain various Vulkan post-processing options. The primarily motivation for this is have a nicer UI for future Vulkan post-processing tools in future (namely vkShade, without having to extend the game menu with a bunch of checkboxes.

As a cool trick, we use eval to export the variable, since right now we only use vkBasalt, and in future we may use vkShade. The export names are just ENABLE_<toolname>, and since <toolname> is what we store in the game config, we can just eval an export string like eval "export ENABLE_VKBASALT=1".

In future, if there are other Vulkan post-processors that require more, we can do some conditional checks to see which post processor is selected, and leave this as our fallback.

There is intentionally no migrateCfg option, as the checkbox for toggling vkBasalt directly controlled ENABLE_VKBASALT. It wasn't stored in the game config, and I didn't want to run the risk of modifying users' custom environment variables. Therefore, users will have to re-enable vkBasalt using this dropdown, which is none by default.

vkShade is not included in the dropdown yet because it is not available without building from source yet. Once a package is at least available on the AUR or Chaotic-AUR, I will include it. The refactor that this PR introduces will make it trivial to introduce though; just add vkShade to the Vulkan Post Processor dropdown.

TODO:

• Logging
• More testing
• Test Non-Steam Games
• Update langfiles

[sonic2kk]

ENABLE_VKBASALT seems to get exported correctly for Steam games, tested with Cookie Clicker. Tested with MangoHUD and adding vkbasalt as a config option.

Tested "Touhou Fumo Racing" as a custom command, it displays vkBasalt as working as well.

For both games, when the post processor is none, vkBasalt is displayed as off, as expected.

[sonic2kk]

Testing is a success on this. Shellcheck looks good on this, langfiles updated. This should make it easier to add vkShade in future :-)

[sonic2kk]

Noticed a typo in the commit name too late, shit. Oh well.