Search: index definition lists as sections

[stsewd]

Currently, we index h tags as sections for all doc types, but for sphinx we additionally index domains (aka roles).

Domains/roles are just like sections, they have a title, content, and they allow you to link to them with an anchor. And sphinx/docutils renders them as a definition list.

So, I think it makes sense to index definition lists as sections for all doctools (or at least the definitions that can be linked), for sphinx projects we will keep indexing domains/roles on their own, so they will keep the current behavior (but kind of like the idea of not having domains/roles at all, since they are specific to sphinx).