WGLWindow lets us use a Windows driver's bindings instead of ANGLE.
This only works if the underlying driver supports OpenGL ES
compatibility.

Also adds the WGL headers, WGL XML, and a specialized WGL loader.

Because of a small driver issue with NVIDIA I added a retry for the WGL
Window initialization.

Bug: angleproject:2995
Change-Id: Ie5148ece470dd03df33015f4919ad1fa79a859ec
Reviewed-on: https://chromium-review.googlesource.com/c/1366021
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>