Moving drag-drop related code into a separate package.

This is per an earlier CR comment "we should probably move all this code to its own package (launcher3.dragndrop) in a separate cl".

I'm not moving DragSource because it's referred from gsa code.

Bug: 22609426
Change-Id: Ia7204dab99c0c395c66b77143a2d60411153f5f3
diff --git a/src/com/android/launcher3/accessibility/LauncherAccessibilityDelegate.java b/src/com/android/launcher3/accessibility/LauncherAccessibilityDelegate.java
index c11aab9..9479685 100644
--- a/src/com/android/launcher3/accessibility/LauncherAccessibilityDelegate.java
+++ b/src/com/android/launcher3/accessibility/LauncherAccessibilityDelegate.java
@@ -20,7 +20,6 @@
 import com.android.launcher3.AppWidgetResizeFrame;
 import com.android.launcher3.CellLayout;
 import com.android.launcher3.DeleteDropTarget;
-import com.android.launcher3.DragController.DragListener;
 import com.android.launcher3.DragSource;
 import com.android.launcher3.Folder;
 import com.android.launcher3.FolderInfo;
@@ -36,6 +35,7 @@
 import com.android.launcher3.ShortcutInfo;
 import com.android.launcher3.UninstallDropTarget;
 import com.android.launcher3.Workspace;
+import com.android.launcher3.dragndrop.DragController.DragListener;
 import com.android.launcher3.util.Thunk;
 
 import java.util.ArrayList;