OpenXR: Windows graphics plugin properly uses HDC instead of HWND;
OpenXR: Windows graphics plugin properly uses HDC instead of HWND;

The HWND was getting passed in directly instead of first converting
it to an HDC.  This was causing SteamVR to fail to create its OpenGL
context.

bjornbytes/lovr,bjornbytes/lovr,bjornbytes/lovr,bjornbytes/lovr,bjornbytes/lovr