Polish the PipMenuView when showing the controls

- Decreases the menu action size
- Wraps custom actions into PipMenuActionView and restricts the size
  to be identical to other PiP actions such as settings and dismiss
- Removed unused pip_menu_activity.xml layout

Screenshot: https://screenshot.googleplex.com/6LFk5WJFfC4FQyA.png
Bug: 179312210
Test: Enter PiP and tap to show controls, see screenshot
Change-Id: I9de63be60ff66ee5198785885a28d495f1fb7af3