Add a unit test to test hiding IME when dismissing biometrics UI

For verifying CL[1] fixed IME flicker issue during biometrics UI
dismissed by focus-lost.

[1]: I541f41832753ea1f4f48f6c4745649606b37d207

Bug: 247705580
Test: atest AuthContainerViewTest#t\
        estDismissesOnFocusLoss_hidesKeyboardWhenVisible
Change-Id: I7622a30778677ed712bbe46d3ea30a0ddb89dfbb