Decoupling some drag and drop code handling

> Removing some special checks around accessibility drag
> Unifying folder alarm code path for accessible and normal DnD
> Maintaining mDragStartTime inside the dragDriver instead of the callers
> Simplifying some accessibility callbacks

Future cl will create a Accessibility DragDriver and unify it with
other DnD flow

Change-Id: I1919ef218de0174678110f271b450bcb9aaf4a5c

src/com/android/launcher3/ButtonDropTarget.java

@@ -155,7 +155,7 @@ public abstract class ButtonDropTarget extends TextView
 
     @Override
     public final void onDragEnter(DragObject d) {
-        if (!d.accessibleDrag && !mTextVisible) {
+        if (!mAccessibleDrag && !mTextVisible) {
             // Show tooltip
             hideTooltip();