Add ImeSubtypeListItem equals and hashCode

This changes the equals method of the ImeSubtypeListItem to take into
account all the fields, and also adds the hashCode implementation for
the class.

Flag: EXEMPT cleanup
Bug: 347693610
Test: atest InputMethodSubtypeSwitchingControllerTest
Change-Id: I78ee0bb2eee56dd98095e60c87472ab57d10d3de