:ls : show "R", "F" for terminal-jobs #10370

This matches Vim behavior. From `:help :ls` :

    R    a terminal buffer with a running job
    F    a terminal buffer with a finished job
    ?    a terminal buffer without a job: `:terminal NONE`

TODO: implement `:terminal NONE`.

ref #10349

src/nvim/channel.c

@@ -762,6 +762,14 @@ static void set_info_event(void **argv)
   channel_decref(chan);
 }
 
+bool channel_job_running(uint64_t id)
+{
+  Channel *chan = find_channel(id);
+  return (chan
+          && chan->streamtype == kChannelStreamProc
+          && !process_is_stopped(&chan->stream.proc));
+}
+
 Dictionary channel_info(uint64_t id)
 {
   Channel *chan = find_channel(id);