Jump-to-heading should place index at nearest heading

[brosasaki]

Purpose of request:
To improve the user experience when using jump-to-heading.

Describe your proposed change:
Make the list interface that appears with jump-to-heading start with the index/highlight over the entry for the nearest heading.

Why do you believe this to be an improvement?
Jump-to-heading is already an incredibly useful feature. However, a limitation of it is that its interface always starts on the first heading of the page. Since this feature is often used on very long webpages (e.g. GNU info manuals converted to a single webpage), this is incredibly inconvenient as it causes the user to lose their place on the page. If the page includes several identical headers, this makes the feature become useless.

Additional context/User story:
I often have trouble with this when browsing a deeply-nested or long page.

Screenshots/Mock ups:
N/A

---

Pre-Build Checklist:

• Discussion has occurred.
• One or more developers have signed off on this change.
• One or more user researchers have signed off on this change.

[aadcg]

@brosasaki sounds like a good suggestion to me.

From a cursory look to the codebase, it should be easy to implement. Any takers?