[pvr] fix marking recordings as watched or unwatched
(fixes #15118)
[pvr] fix bug where the selected item didn't change to the next one
after an item has been marked as watched/unwatched

This emulates the behavior in the video library
[pvr] add helper method to retrieve recording by a file item
[pvr] remove SetPlayCount() wrapper, call the method on the recording
directly
[pvr] fixed folder watched icon appearing only after the folder had
been entered once

This stuff is handled transparently by the list, no need to attempt any
hacks
[pvr] check that the file item has a recording tag before we start
operating on it
[pvr] always update metadata (i.e. play count) for items, not just
the first time an item from that particular folder is encountered
[pvr] hopefully fix the folder watched overlay once and for all. We
now start out by assuming all folders are watched, then as we encounter
unwatched recordings we remember those folders and unmark them at the
end of the method