Extending the grid migration logic to handle density changes

For hotseat migratino, we simply drop the items with least weight
If the workspace row/column decreases by 2 or more, we clear the whole workspace

Bug: 25958224
Change-Id: I7131b955023d185ed10955f593184b9238546dc8

src/com/android/launcher3/InvariantDeviceProfile.java

@@ -73,12 +73,12 @@ public class InvariantDeviceProfile {
     /**
      * Number of icons inside the hotseat area.
      */
-    int numHotseatIcons;
+    public int numHotseatIcons;
     float hotseatIconSize;
     int defaultLayoutId;
 
     // Derived invariant properties
-    int hotseatAllAppsRank;
+    public int hotseatAllAppsRank;
 
     DeviceProfile landscapeProfile;
     DeviceProfile portraitProfile;