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/checkkeys.c

@@ -186,6 +186,7 @@ static void loop(void)
         case SDL_EVENT_TEXT_INPUT:
             PrintText("INPUT", event.text.text);
             SDLTest_TextWindowAddText(textwin, "%s", event.text.text);
+            SDL_CleanupEvent(&event);
             break;
         case SDL_EVENT_FINGER_DOWN:
             if (SDL_TextInputActive()) {