Reset touch location after touch slop is exceeded in recents

There was a jump when a user touch moves over the slop value. To fix
this the location is updated to new y position so that the move
animation of the card after has no visual jump.

Change-Id: Ia9b1d04cc0b2983c2e61114ebbf3bdeb154404e9
Fixes: 35720341
Test: manual - enter recents and slowly drag a card vertically and
notice no jump with the fix, moving after the slop has a consistent
motion

packages/SystemUI/src/com/android/systemui/recents/views/TaskStackViewTouchHandler.java

@@ -279,6 +279,7 @@ class TaskStackViewTouchHandler implements SwipeHelper.Callback {
                         }
 
                         MetricsLogger.action(mSv.getContext(), MetricsEvent.OVERVIEW_SCROLL);
+                        mLastY = mDownY = y;
                     }
                 }
                 if (mIsScrolling) {