Reapply nav hints when systemui crashes or killed

When nav bar is killed or crashes and ime shows, systemui gets restarted
and will not receive any navigation bar hints. Use a callback to wait
for navigation bar to be created and then send the hints to it.

Bug: 112934365
Test: manual
Change-Id: Iee0d76da89bacd99a473ec2e7dec52539e3333ec