Improve VR performance by as much as double, enabling multiview instancing by default and lots of misc changes to the VR render process: - Fix our shaders for multiview instancing to work with the new transform system - Hard code some dumped stencil meshes for Oculus HMDs, reduce render area from 5-14% ( SteamVR doesn't pass us these ) - Remove multi-gpu support, complicates shit and pointless for us to even attempt to maintain - Add SCENE_RTSIZE_VRFRAMEBUFFER and make it adjust to multiview size, avoids allocating 8K render target for framebuffer fetches on VR - Don't attempt to render viewmodel shadows in VR - Fix asserts from C# trying to update viewmodels in VR mode (scenesystem transforms are locked here) - Global.IsRunningInVR doesn't false report if you're running in non VR mode with SteamVR in the background - Generally loads of dead code removal in the render pipeline Co-Authored-By: Sam Pavlovic <sam@sampavlovic.com>