Fix system circular wait during top display focus change

ag/5312657 introduced reporting top focus display change mechanism to ViewRootImpl
for IME window re-focus on top display.

When current focus on external display, system dialog popup on default display,
and then dismiss system dialog, System will possible got circular waiting
for ViewRootImpl lock <-> WMS global lock during reporting top display focus
change to ViewRootImpl & system dialog doing removeWindow for dismissal.

Let WindowState.reportFocusChangedSerialized out of WMS global lock
to fix the case.

Bug: 119658889
Test: manual to verify the issue case can pass
Test: atest ActivityManagerMultiDisplayTests

Change-Id: Ia30a279441def501e53eeee8913d19ac50a620cd