Yellow squiggly lines begone!
Done automatically on .cpp files through `run-clang-tidy`, with manual corrections to the mistakes.
If an import is directly used, but is technically unnecessary since it's recursively imported by something else, it is *not* removed.
The tool doesn't touch .h files, so I did some of them by hand while fixing errors due to old recursive imports.
Not everything is removed, but the cleanup should be substantial enough.
Because this done on Linux, code that isn't used on it is mostly untouched.
(Hopefully no open PR is depending on these imports...)

OpenGL: Check the list of supported AA modes instead of hardcoding

See https://bugs.dolphin-emu.org/issues/13198

bSupports2DTextureStorageMultisample is completely unused, while bSupports3DTextureStorageMultisample is practically unused. In the past, these were checked and fell back to sampler2DMS instead of sampler2DMSArray on GLES 3.1, but this path was removed in f039149198657c1891e1c6462ed30c31ed4b8486 and Dolphin always uses array textures now.

While the NV extension is totally fine, the KHR extension should be able to support more hardware.

For NVIDIA, the hardware either supports both or neither, it just needs a driver from the last two years.
For AMD, the drivers from late 2022-12 seems to bring support for the KHR extension.
For Intel, the KHR is also supported for some years.

Mostly involves moving contents of OGLRender
to OGLGfx and OGLConfig