Implement OpenGL version checking, use it for occlusion queries

Implement OpenGL version checking, use it for occlusion queries

This allows DP to use core features added after 3.2 without crashing,
in this case query buffer objects.

In div0-stable GL_ARB_query_buffer_object was checked but that extension
was written against 4.3 and became part of core in 4.4 so we can just
check for 4.4.

Fixes https://gitlab.com/xonotic/darkplaces/-/issues/176

Moves GL function pointer initialisation to its own function to support
a workaround for NVIDIA's opinion about GL profiles.

Signed-off-by: bones_was_here <bones_was_here@xonotic.au>