filter_chain: allow separate capabilities for filters and conversions
filter_chain: allow separate capabilities for filters and conversions

This will be used for video filters. This is not used for sub filters
and sub sources, as chain of those types do not use conversions.

xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc