Notify listeners when syncing group expansion mgr with the pipeline.

This is a reboot of ag/24148210, but done properly now that we fixed the
behavior in GroupMembershipManagerImpl.

Fix: 293887828
Bug: 282865576
Test: atest GroupExpansionManagerTest & manually verified with the flag
on and off
Flag: NOTIFICATION_GROUP_EXPANSION_CHANGE

Change-Id: If0fee1fa5e46e5760621f8234a169954411e0aa7