Fixes incorrect logspam when the buffer needed to be reset on flushes (which we already were doing, but 52feed04dbf9d487138944ed834bd877620eef74 moved it to after the check was made). This is https://bugs.dolphin-emu.org/issues/10312.
I also converted it to an assert, as if this does happen, things are going to render incorrectly, so we want to make it obvious.
Otherwise, texelFetch() will use an out-of-bounds layer for game textures (that have 1 layer; EFB copies have 2 layers in stereoscopic 3D mode), which is undefined behavior (often resulting in a black image). The fast texture sampling path uses texture(), which always clamps (see https://www.khronos.org/opengl/wiki/Array_Texture#Access_in_shaders), so it was unaffected by this difference.
This regressed in 0a906f553fe7699d1c863a464211f74b6c306a0f, I think (though I haven't confirmed it). Mario Tennis and Luigi's Mansion both use these for some reason (as far as I can tell, the data isn't actually used; it's just extra data included for no reason)
DataReader is generally jank - it has a start and end pointer, but the end pointer is generally not used, and all of the vertex loaders mostly bypassed it anyways.
Wrapper code (the vertex loaer test, as well as Fifo.cpp and OpcodeDecoding.cpp) still uses it, as does the software vertex loader (which is not a subclass of VertexLoader). These can probably be eliminated later.
0e02ddcf52ed86060ac1a0a85fa144738fa5163c removed separate logic for tiled versus non-tiled EFB peek caches, and as part of that made it so that color peeks updated the frame access mask even when a non-tiled cache is in use. However, the same change was not made for depth peeks. I'm not sure if this affected anything in practice.
I originally added these in 2b1d1038a6acf0acf75b03ca93c85de6fe6cdf18, for both the TPipelineFunction and the size. The size was moved into the header in fdcd2b7d009cece6ad090143ce954aed713bb11c (making the size functions obsolete), but it seems that the functions themselves are no longer needed now.
I think I didn't use this approach before because it would have required ComponentFormatTable and ComponentCountRow to be templated, which would end up resulting in lines that were too long and thus wrapped in awkward places. (I *think* they didn't get inferred properly.) Now that we only need TPipelineFunction, the templating is not needed, and this ends up being a more readable version of the version with the wrapper functions.
