fix(messages): recognize cmdline one_key/number prompt State (#34206)

Problem:  Since 48e2a736, prompt messages are handled by an actual
          active cmdline, resulting in `State` no longer being equal
          to `MODE_CONFIRM` which is used in some places. E.g. to
          specify the current `mode()` or to re-emit a confirm message.
Solution: Replace `MODE_CONFIRM` with a new `MODE_CMDLINE` sub-mode when
          `ccline.one_key/mouse_used` is set. Use it to avoid clearing
          mouse_used prompt messages, and to re-emit one_key messages
          (when ext_messages is inactive, for which this is unnecessary).

src/nvim/input.c

@@ -41,8 +41,6 @@ int ask_yesno(const char *const str)
   const int save_State = State;
 
   no_wait_return++;
-  State = MODE_CONFIRM;  // Mouse behaves like with :confirm.
-  setmouse();  // Disable mouse in xterm.
   snprintf(IObuff, IOSIZE, _("%s (y/n)?"), str);
   char *prompt = xstrdup(IObuff);