Add VR support through OpenXR #3174

Job	Run time
Windows (Debug, MSVC, Win32)	8m 50s
Linux (Debug, gcc-5)	8m 35s
Mac (Debug, clang, x86_64)	4m 8s
Windows (Debug, MSVC, x64)	8m 49s
Linux (Debug, gcc-10)	9m 5s
Windows (Release, MSVC, Win32)	8m 51s
Mac (Release, clang, x86_64)	4m 3s
Linux (Debug, clang-9)	8m 39s
Windows (Release, MSVC, x64)	8m 50s
Linux (Release, gcc-5)	7m 8s
Linux (Release, gcc-10)	8m 41s
Linux (Release, clang-9)	8m 38s
Linux (Debug, gcc-10, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	9m 0s
Linux (Release, gcc-10, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	8m 40s
	1h 51m 57s

Provide feedback