gtk4: Add support for GL on Windows

From previous PR !1026 (closed) and should fix #377 (closed) This implements all the workarounds for Windows-specific complications that the GTK GStreamer mediafile implementation also does.

When testing I saw that the wgl* calls were not needed to make a successful run, let me know if I should return them. I will also test on an old surface pro 5 to see if any errors happen on non AMD graphics card. Also, the feature winegl won't build because gstgl does not export egl symbols, at least not on the binary distribution from the website. Should I have built it through gst-build? Should we warn the user in case they try to paint on a surface smaller than the video that they should rescale first on the pipeline? While the gtk backend fixes the “off” colors.