Coarse meshes with high polycount would show as corrupted when GPU
subdivision is used with AMD cards This was caused by the OpenSubdiv
library not taking GL_MAX_COMPUTE_WORK_GROUP_COUNT into account when
dispatching computes. AMD drivers tend to set the limit lower than
NVidia ones (2^16 for the former, and 2^32 for the latter, at least
on my machine).

This moves the GLComputeEvaluator from the OpenSubdiv library into
intern/opensubdiv and modifies it to compute a dispatch size in a
similar way as for the draw code: we split the dispatch size into a 2
dimensional value based on GL_MAX_COMPUTE_WORK_GROUP_COUNT and
manually compute an index in the shader.

We could have patched the OpenSubdiv library and sent the fix upstream
(which can still be done), however, moving it to our side allows us to
better control the GLComputeEvaluator and in the future remove some
redundant work that it does compared to Blender (see T94644) and
probably prepare the ground for Vulkan support. As a matter of fact,
this patch also removes the OpenGL initialization that OpenSubdiv would
do here. This removal is not related to the bug fix, but necessary to not
have to copy more files/code over.