mfvideoenc: Add support for Direct3D11 texture

Merged Seungha Yang requested to merge seungha.yang/gst-plugins-bad:mf-d3d11-interop into master
Initial support for d3d11 texture so that encoder can copy
upstream d3d11 texture into encoder's own texture pool without
downloading memory.

This implementation requires MFTEnum2() API for creating
MFT (Media Foundation Transform) object for specific GPU but
the API is Windows 10 desktop only. So UWP is not target
of this change.
See also

Note that, for MF plugin to be able to support old OS versions
without breakage, this commit will load MFTEnum2() symbol
by using g_module_open()

Summary of required system environment:
- Needs Windows 10 (probably at least RS 1 update)
- GPU should support ExtendedNV12SharedTextureSupported feature
- Desktop application only (UWP is not supported yet)

depends on !464 (merged)

Edited by Seungha Yang

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