Blender Git Loki

Fix T67638: Stretched Camera Background Images

The matrices that projects background images in the 3d view
were incorrect. The root cause was that the coordinate systems were not
respected, that was most noticeable when rotating a stretched image.

We re-validated conversions of coordinate spaces (UV -> Image -> Camera -> Window)
and made sure that the rotation is done in image space.

Reviewed By: campbellbarton

Differential Revision: https://developer.blender.org/D5431