comp: rotate the compute compositor's distortion texture

Some devices like Android smartphones have displays which are
rotated, meaning the compositor needs to rotate its output.

Add support for this to the compute compositor by rotating the
contents of the textures it uses for distortion lookups. This
requires postponing the calculation of that texture and adding
code to recreate it if the rotation changes (which is allowed,
but unlikely to happen in practice.)
25 jobs for compute-rotation-support in 6 minutes and 48 seconds (queued for 5 seconds)