Show confirmation dialog when user tries to skip fingerprint

- After the user finished adding lock screen, if the user tries to skip
fingerprint setup, show a confirmation dialog

bug: 64092225
Test: Manually tested; robolectric tests also added
Change-Id: Iba5088a9db93153988942cf78f11077f427e50cb

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

@@ -139,14 +139,18 @@ public class FingerprintEnrollFindSensor extends FingerprintEnrollBase {
     public void onClick(View v) {
         switch (v.getId()) {
             case R.id.skip_button:
-                setResult(RESULT_SKIP);
-                finish();
+                onSkipButtonClick();
                 break;
             default:
                 super.onClick(v);
         }
     }
 
+    protected void onSkipButtonClick() {
+        setResult(RESULT_SKIP);
+        finish();
+    }
+
     private void proceedToEnrolling(boolean cancelEnrollment) {
         if (mSidecar != null) {
             if (cancelEnrollment) {