On components page, nav shouldn't reflect state unless it updates as you scroll

On the UI components page the left nav will indicate the last link pressed and navigate within the page to the appropriate section. However, as you scroll the page, you pass through other sections, which means the left nav state doesn't reflect where you are in the doc. I think this would be more useable if we either:

- Did not make the left nav indicate navigation within the document
- Made the left nav update as you scroll through sections (AMP bind?)