Remove WebGL 2 support, default to to GLES2 for UWP
Created by: leonkrause
The WebGL 2 rasterizer has too many issues for use in production. Considering it'll be removed once the Vulkan rasterizer hits, it's unreasonable to work further on it.
With this patch only the WebGL 1 rasterizer is available for web export. This also saves about half a MB.