=== Description
Add watchstar icon-button to the sticky header.
== Background / motivation
https://phabricator.wikimedia.org/T294759#7474673
=== Design
the prototype has been updated (remember to log-in): https://di-community-round-2.web.app/Starry_Night_Over_the_Rh%C3%B4ne
{F34722801 width=500}
- Clicking the watch star in the sticky header should behave the same as clicking it in the article toolbar
| watching | unwatching
| {F34728104 width=400} | {F34728106 width=400}
=== Acceptance criteria
[] Add watchstar functionality to the sticky header
[] Under 1200px the sticky header should not display (this seems to have regressed at some point)
[] The watchstar in the sticky header state should be in sync with the one outside the sticky header
== QA steps
* Go to a page which is not watched. Confirm the watchstar at the top of the page is not filled.
* Scroll so the sticky header displays.
* Click the watchstar in the sticky header
* Scroll to the top of the page, the watchstar outside the sticky header should be filled.
* Click the watchstar at the top of the page and scroll down the page to show the sticky header again
* Confirm the watchstar inside the sticky header is not filled.