[Overview Actions] UI update for Landscape.

1. When home screen rotation is allowed, we still have action buttons for landscape, but remove bottom margin to shrink the UI.
2. When home screen rotation is not allowed, we do in-place rotation for overview, where we won't show action buttons.

Test: see demo video: https://drive.google.com/file/d/1G6ihv_DOykx1MLpFAQf3VJHq3D1HotnX/view?usp=sharing
Bug: 153736749

Change-Id: Ia1c7ef8c245ac13bf50adf32ee5114f23e491e75