Update shelf offset earlier when in gesture nav

- Provide a hint to Launcher to indicate it will be resumed when
  swiping home, which allows us to notify sysui before any potential
  pip invocation, reducing the likelyhood of two conflicting animations
  when entering pip

Bug: 156637223
Change-Id: Iae773e1aac88bbea6f74e1d1332417b448126471