Washed out (double gamma correction) on OpenGL

This also happens with the Oculus SDK natively (but only in OpenGL), and the Oculus SDK samples take into account this weird behaviour and manually apply a gamma of 2.2 in the pixel shader (even though the Oculus SDK documentation says it is incorrect to do that). Oculus can get away with that incorrect behaviour in their own API, but you can't do that in OpenXR because all the OpenXR runtimes have to behave the same, whether it is Oculus or SteamVR or whatever.