Use NavBarHelper to keep shared initalizing state between nav/taskbar

* If we switch from taskbar to navbar and state updates, and then
we switch back to taskbar, TaskbarDelegate would have old state
since we stop listening for CommandQueue callbacks.
* NavBarHelper outlives both so it can keep whatever state we need
(and more can be added if necessary into CurrentSysuiState) and
task/navbar can load from that on init

Fixes: 246890611
Test: Couldn't repro bug through device interactions, but
issue via adb (b/246890611#comment8) doesn't repro

Change-Id: I55f888c475fc5d17bd44fb8df73ad5022af421e2