Folder support in Taskbar

- Add TaskbarActivityContext which allows shared Launcher elements to
  "just work" using existing generic ActivityContext.
- TaskbarContainerView extends BaseDragLayer<TaskbarActivityContext>.
- Inflate FolderIcon and Folder using TaskbarActivityContext to be
  shown in TaskbarContainerView.
- Use TaskbarActivityContext's DeviceProfile to determine icon size
  instead of overriding in styles. This also ensures that normal
  BubbleTextView icons have the same size as FolderIcons.

Test: Place a folder in home screen hotseat, ensure it shows up in
taskbar and can be opened, and that apps inside it can be launched
or dragged.
Bug: 171917176

Change-Id: Ic25d2f84bcd7e3399c88989305ea565497c030d9

src/com/android/launcher3/views/BaseDragLayer.java

@@ -206,15 +206,19 @@ public abstract class BaseDragLayer<T extends Context & ActivityContext>
 
     protected boolean findActiveController(MotionEvent ev) {
         mActiveController = null;
-        if ((mTouchDispatchState & (TOUCH_DISPATCHING_FROM_VIEW_GESTURE_REGION
-                | TOUCH_DISPATCHING_FROM_PROXY)) == 0) {
-            // Only look for controllers if we are not dispatching from gesture area and proxy is
-            // not active
+        if (canFindActiveController()) {
             mActiveController = findControllerToHandleTouch(ev);
         }
         return mActiveController != null;
     }
 
+    protected boolean canFindActiveController() {
+        // Only look for controllers if we are not dispatching from gesture area and proxy is
+        // not active
+        return (mTouchDispatchState & (TOUCH_DISPATCHING_FROM_VIEW_GESTURE_REGION
+                | TOUCH_DISPATCHING_FROM_PROXY)) == 0;
+    }
+
     @Override
     public boolean onRequestSendAccessibilityEvent(View child, AccessibilityEvent event) {
         // Shortcuts can appear above folder