mesa: Add GL API support for ARB_copy_image

mesa: Add GL API support for ARB_copy_image

This adds the API entrypoint, error checking logic, and a driver hook for
the ARB_copy_image extension.

v2: Fix a typo in ARB_copy_image.xml and add it to the makefile
v3: Put ARB_copy_image.xml in the right place alphebetically in the
    makefile and properly prefix the commit message
v4: Fixed some line wrapping and added a check for null
v5: Check for incomplete renderbuffers

Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Reviewed-by: Neil Roberts <neil@linux.intel.com>
v6: Update dispatch_sanity for the addition of CopyImageSubData