Texture dumping can already be done using VideoCommon's system (and in fact the same setting already enabled *both* of these). Dumping objects/TEV stages/texture fetches doesn't currently have an equivalent, but could be added to the FIFO player instead.

Currently the logic for addressing the individual TexUnits is splattered all
across dolphin's codebase, this commit attempts to consolidate it all into a
single place and formalise it using our new TexUnitAddress struct.

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.

Cast the variable to the coresponding type.

This header doesn't actually make use of MathUtil.h within itself, so
this can be removed. Many other source files used VideoCommon.h as an
indirect include to include MathUtil.h, so these includes can also be
adjusted.

While we're at it, we can also migrate valid inclusions of VideoCommon.h
into cpp files where it can feasibly be done to minimize propagating it
via other headers.

Makes the global variable follow our convention of prefixing g_ on
global variables to make it obvious in surrounding code that it's not a
local variable.

Normalizes all variables related to statistics so that they follow our
coding style.

These are relatively low traffic areas, so this modification isn't too
noisy.