Reset stack position when all the bubbles are removed

Test: manual
1. have stack on right side of screen
2. dismiss the stack
3. get a new bubble
=> observe flyout animates from correct side of bubble

Bug: 145212704
Change-Id: Ia39ead10a8562a550a0eb069613f071ad53cd253

packages/SystemUI/src/com/android/systemui/bubbles/animation/StackAnimationController.java

@@ -686,6 +686,10 @@ public class StackAnimationController extends
         } else {
             // If there's no other bubbles, and we were in the dismiss target, reset the flag.
             mWithinDismissTarget = false;
+            // When all children are removed ensure stack position is sane
+            setStackPosition(mRestingStackPosition == null
+                    ? getDefaultStartPosition()
+                    : mRestingStackPosition);
         }
     }