Fixed cancel() and commit():

- Call removeSelfLocked() on cancelSessionLocked.
- Call removeSelf() after dispatching the PendingSaveRequest.
- Added a finalizer callback to PendingSaveRequest that calls removeSelf().
- Fixed SaveUi SnackBar so its actions are only triggered once.
- Reused removeSelfLocked() when needed.
- Removed unnecessary {} on some lambdas.
- Removed unnecessary mLock on PendingSaveRequest.
- Removed unnecessary mLock usage on PendingFillRequest.

Test: CtsAutoFillServiceTestCases (including new tests) pass
Test: manual verification

Fixes: 35721501
Fixes: 35844249

Change-Id: I9789218777b62a9558a602b8eaed0714d8b77fa0