Allow exact render-to-tex format mismatches more.

If the right format was used recently, it's still okay.  Also check the
x/y offset to try to find the best match.
Clear vertex attrib arrays before output to screen.

Doesn't seem to help the mis-enabled arrays, though.
Make sure not to leak any enabled vertex arrays.

When returning to EmuScreen, we need to reset any enabled vertex arrays or
we could crash in EmuScreen.  Also, when starting a frame / dirting the
shader, make sure also to toggle the vertex arrays.
Merge pull request #6402 from unknownbrackets/gpu-minor

Fix render-to-tex when format temporarily mismatches