Assume convenience for biometrics not configured in R

This change restores R biometric behavior for devices that:
- Declare FEATURE_FINGERPRINT or FEATURE_FACE
- Have an empty config_biometric_sensors in config.xml
- Report ro.board.first_api_level as 30 (R)

The behavior is restored by assuming that the device has a biometric
sensor of the convenience strength class.

Bug: 200005662
Test: blueline + R vendor w/o the config + S GSI
Change-Id: I70e16089fa4285b1a382d9433af4fc3523b88fc8