Fingerprint Introduction FragmentActivity

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