[wip] Enable CUDA device for video encoder

[Dan-Flores]

This PR adds CUDA support to the VideoEncoder.

• Splits findCodec into findEncoder and findDecoder, and relocates shared component in codecSupportsCudaHardware.

  • The usage of findCodec in SingleStreamDecoder.cpp is updated to use findDecoder().

• Add deviceInterface_ member variable to Encoder which stores an nvenc codec, if available.

• Several tests are updated to test using a CUDA device. Some caveats:

  • Round trip tests using CUDA + FFmpeg4 have much lower pixel accuracy. I want to chalk this up to an FFmpeg bug, since accuracy is significantly better on other versions. As a result, I am skipping CUDA + FFmpeg4 tests.
  • Only mp4, mov, mkv can be tested, since the nvenc_h264 is the only nvenc codec available.
  • To get accurate round trip testing, the crf equivalent for this encoder qp is swapped in during the test and in Encoder.cpp.