Support different multi-window compatibility modes

- Change idea of activity resizablility from true or false to
unresizeable, cropped_windows, resizeable, and resizeable_and_pipable
- Default pre-N apps to cropped_windows mode and N or greater apps to
unresizeable or resizeable depending on the value of resizeableActivity
attribute.
- Mark legacy apps that specify fix orientation or immersive only mode
as unresizeable.
- Change to hide docked stack when unsupported app is the focus app.

Bug: 26774816
Change-Id: Ie473d36ca95f08e9332ab10fd2f0ec17ef50a02f