Fixing widget sheet not scrolled using external mouse

> Fixing crash when some properties are not initialized if draw is not called
> Adding robolectic support for UI testing
> Adding robo tests to verify workspace, all-apps, widgets and folder scrolling

Bug: 147312357
Change-Id: Id7756e07f06396359e441cdff2e4f992bdcb97bb
diff --git a/src/com/android/launcher3/widget/WidgetsFullSheet.java b/src/com/android/launcher3/widget/WidgetsFullSheet.java
index b07a4f4..d7a814a 100644
--- a/src/com/android/launcher3/widget/WidgetsFullSheet.java
+++ b/src/com/android/launcher3/widget/WidgetsFullSheet.java
@@ -87,6 +87,11 @@
         onWidgetsBound();
     }
 
+    @VisibleForTesting
+    public WidgetsRecyclerView getRecyclerView() {
+        return mRecyclerView;
+    }
+
     @Override
     protected Pair<View, String> getAccessibilityTarget() {
         return Pair.create(mRecyclerView, getContext().getString(