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/BiometricEnrollBase.java

@@ -57,6 +57,9 @@ public abstract class BiometricEnrollBase extends InstrumentedActivity {
      * starting the next activity. However, this leads to broken 'Back'
      * behavior. So, now an activity does not finish itself until it gets this
      * result.
+     *
+     * This must be the same as
+     * {@link com.android.settings.password.ChooseLockPattern#RESULT_FINISHED}
      */
     public static final int RESULT_FINISHED = RESULT_FIRST_USER;
 
@@ -78,6 +81,11 @@ public abstract class BiometricEnrollBase extends InstrumentedActivity {
     public static final int LEARN_MORE_REQUEST = 3;
     public static final int CONFIRM_REQUEST = 4;
     public static final int ENROLL_REQUEST = 5;
+    /**
+     * Request code when starting another biometric enrollment from within a biometric flow. For
+     * example, when starting fingerprint enroll after face enroll.
+     */
+    public static final int ENROLL_NEXT_BIOMETRIC_REQUEST = 6;
 
     protected boolean mLaunchedConfirmLock;
     protected byte[] mToken;