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/folder/FolderIcon.java

@@ -754,6 +754,9 @@ public class FolderIcon extends FrameLayout implements FolderListener, IconLabel
     }
 
     public void clearLeaveBehindIfExists() {
+        if (!(getLayoutParams() instanceof CellLayout.LayoutParams)) {
+            return;
+        }
         ((CellLayout.LayoutParams) getLayoutParams()).canReorder = true;
         if (isInHotseat()) {
             CellLayout cl = (CellLayout) getParent().getParent();
@@ -762,6 +765,9 @@ public class FolderIcon extends FrameLayout implements FolderListener, IconLabel
     }
 
     public void drawLeaveBehindIfExists() {
+        if (!(getLayoutParams() instanceof CellLayout.LayoutParams)) {
+            return;
+        }
         CellLayout.LayoutParams lp = (CellLayout.LayoutParams) getLayoutParams();
         // While the folder is open, the position of the icon cannot change.
         lp.canReorder = false;