Add nullability annotations and imports

Bug: 156024031

Test: m -j
Test: atest com.android.server.biometrics
Test: atest com.android.systemui.biometrics
Test: atest CtsBiometricsTestCases
Change-Id: I46a38b6c02452a77c65c3bcb707c5db31c3a4ece
8 files changed