Add an initial doclist extension.

[ericholscher]

This creates a definition list of the document,
and the first 2 paragraphs of the doc to make a nice index.

This is just a first attempt at this,
but something we've wanted to not keep repeating the same content over and over again.

Screenshot

Testing
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.. doclist:: intro/getting-started-with-sphinx

Ideas for improvement

We likely want to have some kind of metadata in the file or similar that's a description that's used first, and then fallback to the top sentence or two, since we don't always want the first 2 sentences to be a good fit for the listing description.

Fixes #10157

[agjohnson]

Looking good so far!

We likely want to have some kind of metadata in the file or similar that's a description that's used first, and then fallback to the top sentence or two, since we don't always want the first 2 sentences to be a good fit for the listing description.

👍 This seems like a really good starting target even. I found most pages have some boilerplate sort of sentences that aren't great descriptions, so I imagine we'll hit this scenario pretty quickly.

I bet we can pretty easily reuse filewide/doc metadata attributes and pull a descriptive title out from docinfo. I like the option of falling back to the first two sentences, at least it's something we can rely on.

[ericholscher]

I think we've refactored this enough to not need this code.