[BiometricsV2] fix enrolling rotate failed

Clean help message during progress changed, and reload help message from
ViewModel in onStart of enrolling page.

Bug: 275513362
Test: atest FingerprintEnrollProgressViewModelTest
Test: enable biometrics v2, and manully rotate screen when help msg
      is shown, and check help msg is kept after screen rotation.
Change-Id: I44220050806038ee62750f8945b8ba8f8bb9c282