Revert^2 "Move cold notification flows to the bg thread."

This reverts commit 2deb82d5.

This was originally reverted due to a build breakage that wasn't caught
by presubmit because another CL that used
NotificationsKeyguardInteractor was merged between presubmit running and
this CL being merged. This is the amended version of the CL.

Bug: 293167744
Bug: 278765923
Flag: ACONFIG com.android.systemui.notifications_footer_view_refactor DEVELOPMENT
Flag: ACONFIG com.android.systemui.notifications_icon_container_refactor DEVELOPMENT
Test: existing tests should still pass, checked some basic functionality
to make sure it looks fine

Change-Id: I3a4e8e1fecd81d7b8e8c681e8ffbc051d1c0ab63