Alternative solution to #114414 which reduces the scope of
textures for which single-channel greyscale optimization
is removed from.
Some byte buffers are converted to float buffers during
color management. These cases should retain support in
the optimal path.
Authored by Apple: Michael Parkin-White
Pull Request: https://projects.blender.org/blender/blender/pulls/114611
ed540b4d3a