New Pipeline: Separate sectioning and sorting steps.

* Fixes a bug where the last NotifSectioner with entries would not have onEntriesUpdated called.
* Changes the contract of onEntriesUpdated so that its called for empty sections.
* Update RankingCoordinator - remove resetClearAllFlags() now that onEntriesUpdated() is called when the section is empty.

Bug: 205348428
Test: atest ShadeListBuilderTest
Change-Id: Idafbc6643aed11f4ee9db23c59a6d5d5da45b09f