This patch doesn't deal with the injection of dependencies
and removal of the global state, but rather moves the code
from DeferredUpdates to the new service essentially as-is,
to simplify review. The changes to inject the various
services needed and make DeferredUpdatesManager a proper
service will be done in follow-ups, to make them easier
to follow.
While almost everything is changed from static to non-static,
DeferredUpdates::$scopeStack remains static as
DeferredUpdatesManager::$scopeStack, just in case multiple
versions of the service are created, to ensure that no
updates are missed.
Bug: T265749
Change-Id: I7f07eddf2fc399b15db4fe9be4c792ef8eb0747b
