Use bilinear filtering to reduce 36 taps to 25 for the regular path.
This works because the middle weights are always between 0 and 1,
allowing texture coordinates to be placed strategically to sample
correct ratios. I'm not sure about the undistort path, so I've left that
alone.
Also remove scaling added in #526, after which weight normalization is
unnecessary. If we want to use or invent an algorithm with alternate
downscaling properties, that's fine, but I don't think we should change
Lanczos scaling to mean something it's not. The scale implementation was
also seen not working when applied directly to scene items because of
assumptions made about the projection matrix.
Intel GPA, SetStablePowerState, Intel HD Graphics 530, D3D11
644x478 -> 1323x1080: 3890 us -> 3401 us
1920x1080 -> 1280x720: 2555 us -> 2261 us
f27ece50c9