Fyrox Game Engine now supports wgpu

The default graphic server is still OpenGL-based, because it is the most stable and well tested. To enable support of wgpu use backend_wgpufeature of the engine. As far as I'm aware wgpu support has some quirks here and there which will be resolved in the future. This post is mostly a call for the community to help with wgpu implementation and make it as stable as OpenGL one. Once it's done, OpenGL impl can be removed entirely.