Now that we have a two-stages GL context creation sequence, we can move
the profile to a pre-realize option, like the debug and forward
compatibility bits, or the GL version to use.
Like what is being done in the X11 and Wayland backends, create the
GdkWin32GLContext in 2 steps, where we only create the actual WGL context
in _gdk_win32_gl_context_realize().
https://bugzilla.gnome.org/show_bug.cgi?id=741946
This adds support for OpenGL to the GDK Windows backend using the WGL API
calls, which enables programs that uses the GTK+ GLArea widgets to work on
Windows as well.
This also adds a simple utility function to query for the version of OpenGL
that is supported by the Windows system, like the one provided by the X11
backend.
Many thanks to Alex (and Emmanuele, who started the OpenGL integration in
GTK+) who offered advice and help along the way, as well as the X11 and
Wayland backend for this work to refer to and to model upon.
https://bugzilla.gnome.org/show_bug.cgi?id=740795
