player: add an auto option to deinterlace

Deinterlacing required that the user set it on/off themselves, but we
actually have handy flags for detecting if a frame is interlaced. So
it's pretty simple to make an auto option using that. Unfortunately,
life is not quite that simple and there are known cases of false
positives from the ffmpeg flags so we can't make auto the default value.
However, it still may have some utility for some people, and the
detection could potentially be improved upon later. Closes #10358.