Notebooks outline
Created by: novoselrok
Fixes #28583 (closed)
See the latest screenshots & videos here: https://sourcegraph.slack.com/archives/C020S8AT3LN/p1649136682840449
Test plan
- Create a notebook with multiple markdown headings
- You should see the level 1 and level 2 headings appear in the outline on the left
- If you click on the heading link in the outline, you should be scrolled to the appropriate heading in the notebook
- As you're scrolling through the notebook you should see the highlighted heading in the outline change