Do not hide notifications on dream

Currently notifications are hidden when dreaming because it is
considered showing keyguard. However, the dream status bar needs
notifications to display the ongoing call chip in the dream status bar.
This change excludes the dreaming case from hiding notifications.

Test: atest KeyguardNotificationVisibilityProviderTest
Test: verified ongoing call chip showing in dream status bar
Fix: 422469252
Flag: com.android.systemui.ongoing_activity_chips_on_dream
Change-Id: Ied7ffc66989f9245c4d9d078b417972782ed6141