Fixing some interaction issues with the PIP menu.

- Due to jank when finishing the PIP menu activity, we handle the
  menu visibility explicitly and keep the menu activity around
  once triggered (until PIP ends), instead of finishing and
  recreating it each time it is invoked.  This also gives us the
  flexibility to control how the animation looks of both the menu
  and individual actions.
- Allow dragging the PIP while the menu activity is showing and
  taking input
- Tapping outside of the PIP now hides the menu

Test: Enable the tap-to-interact in the SysUI tuner and drag while
      the menu is showing.

Change-Id: Iac74710100d793e6825b00c7c0d71b85fb420fa0
Signed-off-by: Winson Chung <winsonc@google.com>