Implements LAUNCHER_ITEM_DROP_COMPLETED event.

Assigns InstanceId to match LAUNCHER_ITEM_DROP_COMPLETED, LAUNCHER_ITEM_DRAG_STARTED events.

Sample Log:
2020-05-01 14:07:53.158 18369-18369/com.google.android.apps.nexuslauncher D/StatsLogManager: LAUNCHER_ITEM_DRAG_STARTED(InstanceId:282)
    # com.android.launcher3.logger.LauncherAtom$ItemInfo@c0711fbd
    application {
      component_name: "com.google.android.apps.maps/com.google.android.maps.MapsActivity"
      package_name: "com.google.android.apps.maps"
    }
    container_info {
      workspace {
        grid_x: 2
        grid_y: 1
        page_index: 0
      }
    }
    is_work: false
2020-05-01 14:07:54.308 18369-18369/com.google.android.apps.nexuslauncher D/StatsLogManager: LAUNCHER_ITEM_DROP_COMPLETED(InstanceId:282)
    # com.android.launcher3.logger.LauncherAtom$ItemInfo@90000206
    application {
      component_name: "com.google.android.apps.maps/com.google.android.maps.MapsActivity"
      package_name: "com.google.android.apps.maps"
    }
    container_info {
      workspace {
        grid_x: 0
        grid_y: 4
        page_index: 0
      }
    }
    is_work: false

Bug: 152978018

Change-Id: Ib4fc860e8080edd407ed15b93f7d55ac31328d11