Implement auto-confirm hinting

(and re-implement the existing PinInputDisplay from scratch with what
I learned about compose)

- refactor the pin input state as a hybrid of digits and clearall events,
  to properly implement the staggered dismiss animation while the last
  pin input is added during a wrong auto-confirm pin entry.
- all pin input display related code is now in its own PinInputDisplay.kt file

Bug: 282730134
Bug: 284429000
Test: Unit tests
Test: manually in ComposeGallery, using auto-confirm with pin-hinting and non-auto-confirm pins  (see recordings added to b/282730134)
Change-Id: I6da01c7ad94f298509e93bde169e00e379211e11