docs: List GL+GLSL versions as parts of a whole.

docs: List GL+GLSL versions as parts of a whole.

Listing the GLSL version as an individual component of a GL version,
separate from the extensions isn't really right. The GLSL changes are
(almost?) entirely comprised of changes listed in the extensions.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>