VideoCommon: Header cleanup

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

(x % y) is not defined in GLSL when sign(x) != sign(y).
This also has the added benefit of behaving the same as sampler wrapping modes, in regards to negative inputs.

Now we require lots of empty functions, but this removes by far more duplicated code.

It's an array of zeroes. There's no need.

Gets rid of magic numbers in cases where the array size is known at compile time.
This is also useful for future entries that are stack allocated arrays as these
functions prevent incorrect sizes being provided.

The hardware backends don't use this shared code any more, and it's not needed for video sw either. So this was just dead code.