Crosses off a lingering TODO.

Also amends a few nearby cases where a u32 cast was being repromoted to
size_t.

They were essentially just pass-though methods

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)

This moves much of the duplicated bounding box code into VideoCommon,
leaving only the specific buffer implementations in each backend.

SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.

Rather than expose the bounding box members directly, we can instead
provide an interface for code to use. This makes it nicer to transition
from global data, as the interface function names are already in
place.

Also remedies places where the video backends and core rely on things
being indirectly included.

Disable bbox