Move flag from systemui to frameworks

Move screenshare_notification_hiding to frameworks to allow usage in
settings

Bug: 323241990
Bug: 316953907
Test: atest SystemUITests
Flag: ACONFIG com.android.server.notification.screenshare_notification_hiding DISABLED
Change-Id: I0394700f526d3761ea2cc7f43141f8fb5563ae4b
9 files changed