TextureCache: Fix blitting filter in Vulkan and correct viewport/scissor calculation when downscaling.

The submodule adds a lot of unneeded bloat due its addition of samples that contain large media files that are difficult to compress.

Also adds descriptions and the settings to the default config.

This only needs to happen once per game boot, so we can just call it
during CreateGPU and be done with it, avoiding the need to call it in
the frontends.