gl: Change gdk_gl_context_check_version()

gl: Change gdk_gl_context_check_version()

Instead of just passing major/minor, pass them twice, once for GL and
once for GLES. This way, we don't need to check for GL and GLES
separately.

If something is supported unconditionally, passing 0/0 works fine.

That said, I'd like to group the arguments somehow, because otherwise
it's just a confusing list of numbers - but I have no idea how to do
that.