win32/gl: Ensure we use the 3.2 core profile
win32/gl: Ensure we use the 3.2 core profile

Emit an error if the profile is different.

This is a follow-up commit to commits cc45e82 (x11/gl: Ensure we use the
3.2 core profile) and 2d9081d (wayland/gl: Ensure we use the 3.2 core
profile), so that we do the same on GDK-Win32.  Update variable names and
comments so that the code is clearer to people, as we still need a
temporary legacy WGL context first before we can use
wglCreateContextAttribsARB() to create a WGL core (3.2+) context.

https://bugzilla.gnome.org/show_bug.cgi?id=741946

Lyude/gtk-,Lyude/gtk-,grubersjoe/adwaita,davidgumberg/gtk,jigpu/gtk,ahodesuka/gtk,jigpu/gtk,chergert/gtk,jigpu/gtk,grubersjoe/adwaita,alexlarsson/gtk,ahodesuka/gtk,jadahl/gtk,davidgumberg/gtk,alexlarsson/gtk,jadahl/gtk,grubersjoe/adwaita,jadahl/gtk,davidgumberg/gtk,jigpu/gtk,davidgumberg/gtk,Adamovskiy/gtk,jadahl/gtk,ahodesuka/gtk,Adamovskiy/gtk,ahodesuka/gtk,Adamovskiy/gtk,chergert/gtk,chergert/gtk,Lyude/gtk-,Lyude/gtk-,Adamovskiy/gtk,Adamovskiy/gtk,davidgumberg/gtk,jigpu/gtk,chergert/gtk,ahodesuka/gtk,jadahl/gtk,Adamovskiy/gtk,Lyude/gtk-,alexlarsson/gtk,alexlarsson/gtk,alexlarsson/gtk,ahodesuka/gtk,alexlarsson/gtk,chergert/gtk,chergert/gtk,jadahl/gtk,davidgumberg/gtk,davidgumberg/gtk,grubersjoe/adwaita,jigpu/gtk,jigpu/gtk,chergert/gtk,davidgumberg/gtk,grubersjoe/adwaita,ahodesuka/gtk,grubersjoe/adwaita,ahodesuka/gtk,chergert/gtk,Lyude/gtk-,jigpu/gtk,jadahl/gtk,Adamovskiy/gtk,alexlarsson/gtk,grubersjoe/adwaita,alexlarsson/gtk,jadahl/gtk,Lyude/gtk-,grubersjoe/adwaita,Lyude/gtk-,Adamovskiy/gtk