Handle swipe down on taskbar to stash

- Moved all touch-to-stash logic to new TaskbarStashViaTouchController
  (handles both tap outside to stash instantly as well as swipe down
  inside to stash after letting go)
- This is a TouchController on TaskbarDragLayer, so it intercepts
  touches from TaskbarView before icons can be dragged during swipe down

Test: swipe up to invoke transient taskbar in an app, swipe down or
touch outside to stash
Flag: ENABLE_TRANSIENT_TASKBAR=true
Fixes: 246631710

Change-Id: I5cf64848bba34ad32fcc80a93fb4f79ebd2c10a7

quickstep/src/com/android/launcher3/taskbar/TaskbarView.java

@@ -419,20 +419,10 @@ public class TaskbarView extends FrameLayout implements FolderIcon.FolderIconPar
         }
     }
 
-    @Override
-    public boolean onInterceptTouchEvent(MotionEvent ev) {
-        mControllerCallbacks.onInterceptTouchEvent(ev);
-        return super.onInterceptTouchEvent(ev);
-    }
-
     @Override
     public boolean onTouchEvent(MotionEvent event) {
-        if (mIconLayoutBounds.left <= event.getX()
-                && event.getX() <= mIconLayoutBounds.right
-                && !DisplayController.isTransientTaskbar(mActivityContext)) {
-            // Don't allow long pressing between icons, or above/below them
-            // unless its transient taskbar.
-            mControllerCallbacks.clearTouchInProgress();
+        if (mIconLayoutBounds.left <= event.getX() && event.getX() <= mIconLayoutBounds.right) {
+            // Don't allow long pressing between icons, or above/below them.
             return true;
         }
         if (mControllerCallbacks.onTouchEvent(event)) {