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.

Fixes a bug on BOTW where some objects were no longer being rendered after blitting

Plus some code deduplication

Blitting or resolving multisampled images requires the dimensions of the src and dst to be equal for valid usage, making them difficult for resolution scaling using the current implementation.

Fixes screenshots at non integer scaling

We don't need to reconstruct new textures every time we ScaleUp/ScaleDown. We can scale up once, and revert to the original texture whenever scaling down.
Fixes memory leaks due to glDeleteTextures being deferred for later handling on some drivers