docs: Import extension spec for GLX_MESA_query_renderer

docs: Import extension spec for GLX_MESA_query_renderer

The enumerated values are currently allocated from Intel's range.

v2: Fix a typo.  Update the list of functions to which the new enums can
be passed.  The "Current" versions were previously missing.  Both things
noticed by Marek.

v3: Fix typo in return type of glXQueryRendererIntegerMESA in the spec
body (noticed by Ken).  Fix typo in issue #14 referencing itself instead
of issue #13 (noticed by Dave).

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Acked-by: Marek Olšák <marek.olsak@amd.com>
Acked-by: Dave Airlie <airlied@redhat.com>