feat(messages): confirm kind for z=, :tselect, inputlist() #32521

Problem:  Messages preceding a `cmdline_show->prompt` event can not be
          distinguished as such when receiving the event. (But since
          `msg_show` handlers should be scheduled, one can already check
          whether a prompt is active when displaying the message.)

Solution: Rather than add a new kind again, use the `confirm` kind.
          Could be seen as slightly misleading where it is more of
          a choice rather than a confirmation, but that already applies
          to `confirm()` as well...

src/nvim/eval/funcs.c

@@ -3556,7 +3556,7 @@ static void f_inputlist(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
     return;
   }
 
-  msg_ext_set_kind("list_cmd");
+  msg_ext_set_kind("confirm");
   msg_start();
   msg_row = Rows - 1;   // for when 'cmdheight' > 1
   lines_left = Rows;    // avoid more prompt