mesa: Implement GL_ANGLE_pack_reverse_row_order

Identical to GL_MESA_pack_invert in effect, just need to check for a
different enum value for GLES vs GL. The spec claims that "OpenGL 1.5 or
OpenGL ES 1.0 are required", but ReadPixels isn't a thing for ES1 so we
only enable it for ES2+.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3156>
5 files changed