This takes care of making the image clearer in some edge cases where the game was already running at near perfect
4:3 with no stretching, and the VI aspect ratio didn't match the XFB by one pixel, making the image stretched and blurry.
-Video: Fix `FindClosestIntegerResolution() using the window aspect ratio and not the draw aspect ratio, causing it to prefer
stretching over black bars in cases when it wasn't desirable.
Almost all the virtual functions in Renderer are part of dolphin's
"graphics api abstraction layer", which has slowly formed over the
last decade or two.
Most of the work was done previously with the introduction of the
various "AbstractX" classes, associated with texture cache cleanups
and implementation of newer graphics APIs (Direct3D 12, Vulkan, Metal).
We are simply taking the last step and yeeting these functions out
of Renderer.
This "AbstractGfx" class is now completely agnostic of any details
from the flipper/hollywood GPU we are emulating, though somewhat
specialized.
(Will not build, this commit only contains changes outside VideoBackends)
