Turn session actions on by default and add layout flag

Adds a separate flag to enable the new media layout, which will also
require the session actions flag to be enabled.

Session actions flag will be enabled by default. If the new layout flag is
off, this will show the actions in the old layout, ordered like: custom 2,
previous, play, next, custom 1

Bug: 203800354
Bug: 209657555
Test: manual - flip flags, check controls
Test: atest

Change-Id: I0683d38939341631d6c48b266c0c35056344cfa6