direct3d11: fix leak when using NVIDIA Super Resolution

This is the 4.0 version of !3716 (merged)

Rather than forcing the filling of a whole texture and then place it, as in !3664 (closed), we convert to RGBA when doing the upscaling. This also avoids the leak and it keeps the SPU positioning/stretching correct.

There's also an extra fix for sources with a non 1:1 SAR (as some DVDs).