player: reduce impact of blocking filters

Some filters may block the playloop for a longer time. For example, if a
decoder fails to decode anything and somehow just discards packets, the
filter graph would run (in a blocking manner) until all packets are
read, which could take a longer time if the demuxer thread is fast
enough.

Make it exit every 100ms. That should at least give the user a chance to
stop playback.

Filtering could run on a different thread, but I don't see much value in
doing that in the general case. It would just waste a thread. Although
being able to use mp_filter_graph_interrupt() would be slightly nicer
than such a timeout mechanism. Decoding in particular can actually use a
separate thread (--vd-queue-enable), but again, this is not enabled by
default, because it just wastes a thread.

Like the previous f_decoder_wrapper commit, this is probably a sin.

player/loadfile.c

@@ -1399,6 +1399,7 @@ static void play_current_file(struct MPContext *mpctx)
     mpctx->seek = (struct seek_params){ 0 };
     mpctx->filter_root = mp_filter_create_root(mpctx->global);
     mp_filter_root_set_wakeup_cb(mpctx->filter_root, mp_wakeup_core_cb, mpctx);
+    mp_filter_graph_set_max_run_time(mpctx->filter_root, 0.1);
 
     reset_playback_state(mpctx);