Create a listing link preprocessor to address the in-text linking issue

[mianlang]

Following #4271.

It works by handling the pattern Listing\s(\d+-\d+) and replacing it with <a href="#listing-$1" class="listing-link">.

However, cross-chapter references aren't handled yet–I'm not quite sure how to approach that part at the moment.

And cross-chapter references are handled by a HashMap dictionary.

[mianlang]

One possible approach: first collect all listing numbers along with their corresponding filenames and store them in a dictionary. Then, during the replacement phase, look up the referenced filename in that dictionary using the listing number, take the current filename into account, and construct the correct href.

[mianlang]

I got it working – it should now address the in-text linking issue (which is quite exciting from my point of view, though it doesn't affect the print version). Let me know if anything needs to be adjusted to move forward, such as code style, module naming, code organization, or tests – which I suppose there should be quite a bit of.

Just to share one thing I ran into during the process: I'm not sure how to efficiently debug mod.rs. My current loop is: make a change, run cargo install --locked --path packages/mdbook-trpl, rebuild with mdbook build, then check the output HTML. I imagine there must be a more idiomatic or streamlined way.

A fix on broken links was also included, since otherwise the lint would fail. #4295 fixes that, and I'll rebase main after it's merged. This also shows that in the future, if someone forgets to update an outdated listing reference, linkcheck.sh will complain.

Note: cases like references to multiple listings (e.g. "Listings 10-16, 10-17, and 10-23" in Ch. 10) aren't handled yet. Also, this doesn't fully address #921, as neither the referencing of figures nor the figure-with-number component itself has been implemented.

[chriskrycho]

Excellent! I’ll try to take a look early next week or over the weekend, though I am also shifting my focus elsewhere and taking some time off for the next four weeks, so I may be quite slow to respond and iterate for that period of time.