macOS: Fix problems with OpenGL context creation on macOS

Fixes #5811 (closed)

• The GL version reported by epoxy seems to depend on the current GL context, so the GL context to create should be the one determined by gdk_gl_context_get_matching_version

  In my environment, the call to gdk_gl_context_get_matching_version reports GL version 3.2, and the call to gdk_gl_version_init_epoxy reports GL version 4.1, I believe this move is in line with the original intent of using the best possible GL version.

• Fix a bug in error checking conditions. This avoids unintentional Legacy of the created OpenGL context.

Related:

• !6016 (closed)
• #5811 (comment 1754297)