1. Fix backstacks after enrolling finish
2. Support skipFindSensor and skipIntro
Bug: 260957939
Test: Manually test it on different sensor devices
Change-Id: I4061e29999a47bf4859d6562ad82330fb0f6f620
Introducing MVVM architecture & fragments to biometric settings.
Here, we modify the first page of FingerprintEnrollIntroduction to use
new MVVM with Fragment architecture.
And with this new architecture, unit test and screen order will be
easier to be written or changed.
Bug: 236072782
Test: atest FingerprintEnrollmentViewModelTest AutoCredentialViewModelTest
FingerprintEnrollIntroViewModelTest FingerprintRepositoryTest
Change-Id: Icf12c91625db86c2c99081a0108203e607e77f74
