Dynamically allocate long text for SDL_EVENT_TEXT_INPUT events

This prevents input text from being split across Unicode combining or modifier characters, and in practice allocations will rarely happen.

test/checkkeysthreads.c

@@ -187,6 +187,7 @@ static void loop(void)
             break;
         case SDL_EVENT_TEXT_INPUT:
             PrintText("INPUT", event.text.text);
+            SDL_CleanupEvent(&event);
             break;
         case SDL_EVENT_MOUSE_BUTTON_DOWN:
             /* Left button quits the app, other buttons toggles text input */