Start home activities for all displays on boot

We were only starting home activity on default display when
system boot up. After system booted, home activities would be
started when new displays added. But in some cases, there
are more than one displays being ready before boot completed.
So it ended up with no home activities on secondary displays.

Making sure home activities can be launched on all displays
on boot now.

Also checks finishing booting when all resumed activities
on all displays are idle.

Bug: 111363427
Test: Manual
Test: atest ActivityStackSupervisorTests

Change-Id: I2291ce967bc6f2f03ca7f680c3d6a2d8e8f3cd08