On multi-user bouncer auth, animate sub views

Instead of the entire view, to make sure the background
color stays consistent.

Fixes: 338197784
Test: manual, look for black flicker on bottom of screen
Flag: EXEMPT bugfix
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:c450457180829afc139dd87c03a6660cf0006d2e)
Merged-In: Idf066d937b565637cdda12ad50dcee3dce46796a
Change-Id: Idf066d937b565637cdda12ad50dcee3dce46796a

packages/SystemUI/src/com/android/keyguard/KeyguardSecurityContainer.java

@@ -1097,7 +1097,8 @@ public class KeyguardSecurityContainer extends ConstraintLayout {
             int yTranslation = mResources.getDimensionPixelSize(R.dimen.disappear_y_translation);
 
             AnimatorSet anims = new AnimatorSet();
-            ObjectAnimator yAnim = ObjectAnimator.ofFloat(mView, View.TRANSLATION_Y, yTranslation);
+            ObjectAnimator yAnim = ObjectAnimator.ofFloat(mViewFlipper, View.TRANSLATION_Y,
+                    yTranslation);
             ObjectAnimator alphaAnim = ObjectAnimator.ofFloat(mUserSwitcherViewGroup, View.ALPHA,
                     0f);