Also inline str_format().

There are several issues with str_format() and str_format_meta():
 - the current playlist item is used rather than the actual input,
 - the playlist gets activated for nothing,
 - they assume the output does not outlive to the input (item).

This mostly reverts commit cccd51a5.

pl_Get() can only be used in interfaces, playlist and ML code.

This could crash. The playlist needs to be started (at least until
someone resolves bug #5460).

ml_AttributeIsString() defines String as 1 and Integer as 0.
The switch/case was just doing the opposite...

vlclua_playlist_add_internal() requires the playlist only if there is
no parent item. There is always a parent item when demuxing.

pl_Get() has side effects.

This does not really work anyway.

Sorry...

The thread is not cancelled (ever since vlc_clone() replaced
vlc_thread_create()).

This is simpler and more consistent.

In the original stream_Demux (from 2004), there was a lock. But then
it vanished in a big input "rework"... Anyway, killing the demux
explicitly should not be needed: The underlying stream will return EOF
and any sane demux will return on EOF.

This is for backward compatibility with existing VLC playlists and
VLC playlist generators.

So the code is reusable for radio device nodes.

Signed-off-by: Konstantin Pavlov <thresh@videolan.org>