Tweaks to integrate BiometricEnrollActivity to SUW

- Default backup screen lock type to PIN when in SUW
- Propagate the result codes in BiometricEnrollIntroduction, so that
  when the user hits back, SUW will get RESULT_CANCELED
- Follow-up change that was missed in ag/6664364 to not start activity
  when neither fingerprint nor face is available

Test: Manual
Bug: 120797018
Change-Id: I6d4f662928451fb86f301ddb5c6586622c7e6cf7