Drop DirectXTex dependency or use nugget version of DirectXTK instead

[ali-alidoust]

We can change the code so that FFMPEG directly uses a memory mapped ID3D11Texture2D instead of copying it using DirectXTex. It might give some speed boost and remove the dependency to DirectXTex.

If it's not possible, we should at least remove the files from the project and use nugget version of DirectXTK. We can use the CaptureTexture function from ScreenGrabber.cpp to implement the same functionality.