Adding A feature flag to disable widgets  and a corresponding build
target Launcher3Go without widgets support

Bug: 62353159
Change-Id: Ia03d2235a9bcf75f9ef191924f81630e63a2c684
diff --git a/src/com/android/launcher3/LauncherModel.java b/src/com/android/launcher3/LauncherModel.java
index 82bee0e..f1638fd 100644
--- a/src/com/android/launcher3/LauncherModel.java
+++ b/src/com/android/launcher3/LauncherModel.java
@@ -133,7 +133,7 @@
         }
     };
 
-    public interface Callbacks {
+    public interface Callbacks extends LauncherAppWidgetHost.ProviderChangedListener {
         public boolean setLoadOnResume();
         public int getCurrentWorkspaceScreen();
         public void clearPendingBinds();
@@ -159,7 +159,6 @@
                 HashSet<String> packageNames, HashSet<ComponentName> components,
                 UserHandle user);
         public void bindAppInfosRemoved(ArrayList<AppInfo> appInfos);
-        public void notifyWidgetProvidersChanged();
         public void bindAllWidgets(MultiHashMap<PackageItemInfo, WidgetItem> widgets);
         public void onPageBoundSynchronously(int page);
         public void executeOnNextDraw(ViewOnDrawExecutor executor);