Add VR support through OpenXR #3176

Job	Run time
Windows (Debug, MSVC, Win32)	14m 40s
Mac (Debug, clang, x86_64)	9m 10s
Windows (Debug, MSVC, x64)	15m 33s
Mac (Release, clang, x86_64)	8m 3s
Linux (Debug, gcc-5)	8m 13s
Linux (Debug, gcc-10)	12m 12s
Windows (Release, MSVC, Win32)	23m 50s
Linux (Debug, clang-9)	12m 46s
Windows (Release, MSVC, x64)	27m 0s
Linux (Release, gcc-5)	6m 42s
Linux (Release, gcc-10)	7m 53s
Linux (Release, clang-9)	17m 41s
Linux (Debug, gcc-10, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	13m 36s
Linux (Release, gcc-10, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	10m 26s
	3h 7m 45s

Provide feedback