Move widget files into widget folder + add tests.

I will use the newly created LauncherAppWidgetProviderInfoTest in a follow-up CL to add tests for the newly added widget sizing APIs.

Test: Automatic: Ran all robolectric tests in launcher3,
      Manual: Added a widget, edited the widget, removed the widget
Bug: 179807199
Change-Id: I540b2dbe284c6eb5aa2466a1d13a9581ee59425b
diff --git a/src/com/android/launcher3/SecondaryDropTarget.java b/src/com/android/launcher3/SecondaryDropTarget.java
index 7276887..4fd87cb 100644
--- a/src/com/android/launcher3/SecondaryDropTarget.java
+++ b/src/com/android/launcher3/SecondaryDropTarget.java
@@ -46,6 +46,7 @@
 import com.android.launcher3.model.data.LauncherAppWidgetInfo;
 import com.android.launcher3.util.PackageManagerHelper;
 import com.android.launcher3.util.Themes;
+import com.android.launcher3.widget.LauncherAppWidgetProviderInfo;
 
 import java.net.URISyntaxException;