[BiometricsV2] Fix intro overlap enrolling page

Fix fragment overlapped if user rotates device on findSensor page, then
enter enrolling page and back again.

It is because the flag isFirstFragmentAdded is not saved and restored
after activity recreated

Bug: 288212767
Test: atest FingerprintEnrollmentActivityTest
Test: atest FingerprintEnrollmentViewModelTest
Test: atest biometrics-enrollment-test
Test: Manually test this scenario
Change-Id: I5b582582d97caac2488b787f551c50abec9f810c