[BiometricsV2] Refactor EnrollIntroViewModel

1. Refactor FingerprintEnrollIntroViewModel to kotlin and replace
   LiveData as Flow
2. Set importantForAccessibility to sud_scroll_view (porting solution of
   b/244595576 into fingerprint enrollment v2)

Bug: 286198097
Test: atest -m FingerprintEnrollIntroViewModelTest
Test: atest -m FingerprintEnrollmentActivityTest
Test: atest -m biometrics-enrollment-test
Change-Id: Idd4e9d77d040d7efd61342284d7b6a493a20a539