Add @hide to the biometric interfaces

This change allows the framework to depend on biometric AIDL types, for
example: `android.hardware.biometrics.fingerprint.PointerContext`.

The dependency can be introduced with a `-java-source` target, for
example: `:android.hardware.biometrics.common-V3-java-source`.

The "@hide" annotation informs Metalava that these types are not a
public API (not part of the SDK).

Bug: 218388821
Test: m android.hardware.biometrics.common-update-api
Test: m android.hardware.biometrics.face-update-api
Test: m android.hardware.biometrics.fingerprint-update-api
Change-Id: Ib3327594c64dbb800b9d1744869ceb490d63e553