Apply "Extract dashboard section into its own component"

This reverts commit 543a9f8ce35dee866aba6323d807fbb04c4e7c24 and adds
the fix on top.
Original change had to be reverted because the empty state slot was
not being applied 2 levels up.
Hence add a pass through slot in gr-change-list.

Testing mainly relies on unit tests and manually verifying slots are
rendered on the dashboard.
Specific steps for testing are:
- Verify special empty slots for Your Turn and Outgoing Review section
(screenshot attached)
- Verify generic empty slots for Incoming Review (screenshot attached)
- Add missing test coverage for showStar and showNumber property in
 GrChangeList test
- Fix regression in change list navigation Change 329951
- Add Shadow DOM UT for GrChangeList Change 329962
- Add Shadow DOM UT for GrChangeListItem Change 329964
- Hovercard actions from the dashboard (Add to AS / Remove from AS)
- Dashboard when logged out, star column is hidden (screenshot attached)
- Custom dashboard (screenshot attached)

Release-Notes: skip
Screenshots: https://imgur.com/a/IlCH1yc
Change-Id: I7fedb6cc52b819960a17c6f9cfd6bd310deb6e21
diff --git a/polygerrit-ui/app/constants/constants.ts b/polygerrit-ui/app/constants/constants.ts
index 3024597..6ed9646 100644
--- a/polygerrit-ui/app/constants/constants.ts
+++ b/polygerrit-ui/app/constants/constants.ts
@@ -305,3 +305,5 @@
 export const RELOAD_DASHBOARD_INTERVAL_MS = 10 * 1000;
 
 export const SHOWN_ITEMS_COUNT = 25;
+
+export const WAITING = 'Waiting';