Minor changes on AutoFill Save UI.

- Fixed subtitle layout.
- Added a Shell command to change snackbar lifetime (so CTS tests can verify
  it's dismissed).

BUG: 35727295
Test: CtsAutoFillServiceTestCases (with new tests) pass
Test: manual verification

Change-Id: Ie6d42c94599ad59a319ca6f6a1ab02882f8d5f81