Add flag for fixing Avalanche HUN replacement when critical HUN arrives

The existing behavior: FSI and Remote Input activated HUNs are never
replaced by another HUN.
Behavior wanted: any HUN can be replaced by critical HUNs (FSI and
incoming calls)

Bug: 403301297
Test: Manual, TheFlippinApp
Flag: com.android.systemui.avalanche_replace_hun_when_critical
Change-Id: I91b3bed755f395d944a584ca98ada91816475f2b