perf ui browser hists: Provide feedback on unhandled hotkeys

Don't just eat unknown keys without providing visual feedback and
instructions on how to see which ones are assigned.

Suggested-by: Ingo Molnar <[e-mail]>
Tested-by: Ingo Molnar <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: James Clark <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Kan Liang <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/ui/browsers/hists.c

···
 			/* Fall thru */
 		default:
 			helpline = "Press '?' for help on key bindings";
+			ui_browser__warn_unhandled_hotkey(&browser->b, key, delay_secs,
+							  ", use 'h'/'?'/F1 to see actions");
 			continue;
 		}
 
···
 		case CTRL('c'):
 			goto out;
 		default:
+			ui_browser__warn_unhandled_hotkey(&menu->b, key, delay_secs, NULL);
 			continue;
 		}
 	}
···
 	struct popup_action action;
 	char *br_cntr_text = NULL;
 	static const char help[] =
-	" q             Quit \n"
+	" q/ESC         Quit \n"
 	" B             Branch counter abbr list (Optional)\n";
 
 	browser = hist_browser__new(hists);
···
 
 		switch (key) {
 		case 'q':
+		case K_ESC:
 			goto out;
 		case '?':
 			ui_browser__help_window(&browser->b, help);
···
 			}
 			continue;
 		default:
-			break;
+			ui_browser__warn_unhandled_hotkey(&browser->b, key, 0,
+							  ", use '?' to see actions");
+			continue;
 		}
 	}