Fix couple of drag and drop issues from transient taskbar

- Use tappableElement insets instead of systemBars, so that the drag
  layout highlight goes edge to edge
- Allow launcher to pass an intent extra for "DISALLOW_HIT_REGION" so
  that we don't accept drag events over the transient taskbar region

Test: manual with persistent vs transient taskbar
Bug: 269814838
Bug: 259645384
Change-Id: I022f1c7a07b146fcde33cfb2e742a3b3d8e25064