obs-qsv11: Use d3d9 allocator on Win7

Use a d3d9 device and allocator to encode in QSV.

This fixes a random crash that could only happen on Windows 7. The QSV
Deviced returned a DEVICE_FAILURE after a random amount of time with the
old method.

This fix is totally based on Shinck's QSVHelper.exe patch for OBS
Classic (see
https://obsproject.com/forum/threads/0-633b-qsvhelper-exe-was-killed-encode-failed.19230/page-3#post-161984
for more information)

This is more like a proof of concept, but that fix is currently stable
and tested more than 50 hours, with a single session of +14 hours.

That commit doesn't respect all OBS Guidelines. It is currently
recommended to wait for a more "cleaner" implementation.

plugins/obs-qsv11/QSV_Encoder_Internal.h

@@ -108,5 +108,6 @@ private:
 	mfxBitstream                   m_outBitstream;
 	bool                           m_bIsWindows8OrGreater;
 	bool                           m_bUseD3D11;
+	bool                           m_bD3D9HACK;
 };