Fix issue where highlight was drawing without bottom inset on one side only

- If a drag is started over home, we ignore the bottom insets to
  draw the highlight the full height, however we were still handling
  taskVanished even if there is no drag in session, which meant that
  setForceIgnoreBottomMargin(true) could be called before the next
  drag session which does not reset it (it only reset it on hide()).

  This change properly skips handling taskVanished while not dragging
  and also resets setForceIgnoreBottomMargin() when the highlights
  should be showing for both tasks
- Also add some descriptive logging for the drag flags

Flag: EXEMPT bugfix
Bug: 350016003
Test: Drag floating assistant over home, then over another app
Change-Id: I175610a643b4a69850bc3b289032f1b3b8524a21