Create tests and test FFmpeg against other backends

The goal of this task is to identify testing tasks to ensure that the FFmpeg backend is on par with native backends for multimedia features, including encoding and decoding.

One starting point is to create a table tests we need to do, including multimedia feature, platforms, HW accel backends, if HW texture conversion is enabled or not, CPU memory usage, GPU memory usage, CPU processor usage, GPU processor usage, media files tested with, include normal HD and 4K@60Hz.

Talk with artemiy to get ideas on how this can look.

Tasks for CPU/GPU usage and codec support is already created. These may be split into smaller tasks per platform.