8/n: Update biometric utils to have sensorId-specific files

New HAL interfaces have a strongly defined notion of sensorId whereas
existing interfaces do not. This change does the following:

1) FingerprintUtils/FaceUtils is updated to contain singleton
   instances for each sensorId. The retrieved instance is still
   a utility class for a single sensor
2) Existing devices with old HALs will continue to use
   settings_fingerprint.xml and settings_face.xml
3) Devices with new HALs will use sensorId-specific files, e.g.
   on a device where the fingerprint sensorId=0 and face sensorId=1,
   the below files will be used:
   settings_fingerprint_0.xml, settings_face_1.xml
4) Updated existing AIDL provider to use sensor-specific utils

Bug: 170497736
Test: Enrollments on existing devices not affected

Change-Id: I5c48ab927d0450820f165707d60e0710e86be5e4