Support autofilling a remote app.

This is only intended for system components like SystemUI.

Design: go/sysui-underlay

Bug: 403422950
Flag: android.view.contentcapture.flags.enable_system_ui_underlay
Change-Id: Ie58c804665d91f4e91a9fdf37687b63efac5ca54
Test: atest FrameworksCoreTests:ActivityThreadTest