Reinstate copy-able anchors for headings in spec documents

[azaroth42]

For example, https://iiif.io/api/presentation/3.0/#type works to take you to the definition of the type property, but it's not in the table of contents and the selectable link has disappeared in the new website.

It does work on hover for the main links:

But not for things like the property names in the specs:

[hadro]

Thanks for the clarification, this is addressed in IIIF/api#2078
I added hover through h5
Deployment example is here: https://preview.iiif.io/api/heading_anchor_fix/presentation/3.0/#type

[hadro]

This is deployed!