autofillHints and importantForAutofill only used in API 26 and higher but we still can use it in API < 26 without crash (你可以在这个答案中看到) (it don't crash but ofcourse it don't have any effect with API < 26)
tool:...只是用来使 IDE 不发出警告,它不会影响应用程序运行时的任何东西,所以 tools:ignore="Autofill不会帮助你隐藏自动填充提示