New behavior for docked stack when going home

- We keep the docked stack visible when home task is visible even
though it's not resizable.
- We introduce the a new concept called "minimizing" the docked stack,
which happens when going home. In this state, the docked stack is
clipped of almost completely.
- To achieve that, we introduce TaskStackBoundsAdjustController,
which adjusts the bounds of the docked stack when minimized. Also,
migrate the IME handling to this new class.
- We also need to inform SysUI that it is now minimized so it can
remove the drag affordance on the divider, and also make it a bit
smaller.
- When we detect an app transition, we check whether the home stack
gets visible/invisible. We then start an animation which runs in
sync with the normal app transition. For that we introduce
DockedStackDividerController.animate(), which performs the animation.

Bug: 27137961
Change-Id: I8623bc73cc6872bf28c5b1b8d5795974576811b2