Added new Autofill APIs to get name of id used on android:text.

Such resource id is useful to help the autofill service heuristics to figure out
the meaning of the labels without relying on their localized text. For example,
the id could be "username", while the text could be "Nome do usuario".

Test: atest CtsAutoFillServiceTestCases:LoginWithStringsActivityTest

Fixes: 71552872

Change-Id: I13f7080fb3c67f91492a113115ffa43d185d192a