Use footer bar button to skip remote LSKF validation for expressive

theme

Additional changes:
* Refactored showCancelButton evaluation logic
* Renamed confusing "enable" variable in
  `updateRemoteLockscreenValidationViews`

Flag: EXEMPT for expressive style customization
Bug: 415202233
Test: atest ConfirmLockPasswordTest
Test: atest ConfirmLockPatternTest
Test: atest ConfirmCredentialTest
Test: Manually went through Remote LSKF validation flow in SUW and
confirmed LSKF in Settings

Change-Id: I93b81d6c0c793bfc25007bde293cf9aa1dd92234