Implement LAUNCHER_ITEM_DRAG_STARTED event.

* Fixes null component issue when ItemInfo object copiedFrom.
* Fixes missing container when item is dragged from hybrid hotseat.

Sample Logs:
2020-04-30 14:09:45.499 30472-30472/com.google.android.apps.nexuslauncher D/StatsLogManager: LAUNCHER_ITEM_DRAG_STARTED
    # com.android.launcher3.logger.LauncherAtom$ItemInfo@260f31f8
    application {
      component_name: "com.android.chrome/com.google.android.apps.chrome.Main"
      package_name: "com.android.chrome"
    }
    container_info {
      workspace {
        grid_x: 2
        grid_y: 2
        page_index: 2
      }
    }
    is_work: false

2020-04-30 14:23:15.230 31320-31320/com.google.android.apps.nexuslauncher D/StatsLogManager: LAUNCHER_ITEM_DRAG_STARTED
    # com.android.launcher3.logger.LauncherAtom$ItemInfo@608f101
    application {
      component_name: "com.google.android.gm/.ConversationListActivityGmail"
      package_name: "com.google.android.gm"
    }
    container_info {
      hotseat {
        index: 1
      }
    }
    is_work: false

Bug: 152978018

Change-Id: I3d3ce213fd2fc6eb5ffb239e048ceb7c0fa88b53

src/com/android/launcher3/Workspace.java

@@ -79,6 +79,8 @@ import com.android.launcher3.folder.PreviewBackground;
 import com.android.launcher3.graphics.DragPreviewProvider;
 import com.android.launcher3.graphics.PreloadIconDrawable;
 import com.android.launcher3.icons.BitmapRenderer;
+import com.android.launcher3.logging.StatsLogManager;
+import com.android.launcher3.logging.StatsLogManager.LauncherEvent;
 import com.android.launcher3.logging.UserEventDispatcher;
 import com.android.launcher3.model.data.AppInfo;
 import com.android.launcher3.model.data.FolderInfo;
@@ -409,6 +411,10 @@ public class Workspace extends PagedView<WorkspacePageIndicator>
 
         // Always enter the spring loaded mode
         mLauncher.getStateManager().goToState(SPRING_LOADED);
+        StatsLogManager.newInstance(getContext())
+                .log(
+                    LauncherEvent.LAUNCHER_ITEM_DRAG_STARTED,
+                    dragObject.originalDragInfo.buildProto(null));
     }
 
     public void deferRemoveExtraEmptyScreen() {