2/n: Add default implementation for multi-biometric enroll

1) Adds a layout for multi-biometric selection in BiometricEnrollActivity
2) Adds widgets for checkboxes
3) Shows ConfirmLock*/ChooseLock* for multi-biometric devices in
   BiometricEnrollActivity
4) finish()'s when loses foreground
5) Adds default string for ChooseLock* and multi-biometrics, e.g.
   "Set up Password + Biometrics", as well as associated plumbing
   to bring the user back to BiometricEnrollActivity once the
   credential is enrolled
6) When max templates enrolled, checkbox becomes disabled and
   description string is updated

Bug: 162341940
Bug: 152242790
Fixes: 161742393

No effect on existing devices with the following:
Test: adb shell am start -a android.settings.BIOMETRIC_ENROLL
Test: SUW
Test: make -j RunSettingsRoboTests

Exempt-From-Owner-Approval: Biometric-related change
to EncryptionInterstitial

Change-Id: I855460d50228ace24d4ec5fbe330f02ab406cc02

src/com/android/settings/biometrics/fingerprint/FingerprintEnrollFindSensor.java

@@ -63,7 +63,7 @@ public class FingerprintEnrollFindSensor extends BiometricEnrollBase {
 
         // This is an entry point for SetNewPasswordController, e.g.
         // adb shell am start -a android.app.action.SET_NEW_PASSWORD
-        if (mToken == null && BiometricUtils.containsGatekeeperPassword(getIntent())) {
+        if (mToken == null && BiometricUtils.containsGatekeeperPasswordHandle(getIntent())) {
             final FingerprintManager fpm = getSystemService(FingerprintManager.class);
             fpm.generateChallenge((sensorId, challenge) -> {
                 mToken = BiometricUtils.requestGatekeeperHat(this, getIntent(), mUserId, challenge);
@@ -79,6 +79,9 @@ public class FingerprintEnrollFindSensor extends BiometricEnrollBase {
         } else if (mToken != null) {
             // HAT passed in from somewhere else, such as FingerprintEnrollIntroduction
             startLookingForFingerprint();
+        } else {
+            // There's something wrong with the enrollment flow, this should never happen.
+            throw new IllegalStateException("HAT and GkPwHandle both missing...");
         }
 
         View animationView = findViewById(R.id.fingerprint_sensor_location_animation);