Add IHomeTransitionListener to shell.

This allows launcher to listen in on any transitions that include the home
activity.

Bug: 279514548
Bug: 284474103
Test: Enable ENABLE_HOME_TRANSITION_LISTENER in launcher dev options
      App launch => Hotseat -> Taskbar -> Stash
      Launch translucent activity => No animation
      Go home from app => Taskbaer -> Hotseat

Change-Id: I574b8164bd61475ba05bbb86aef358f364227e66