Fixes to "staying on the same page functionality" (version with tests removed)

[ilyagr]

This is #7350 with the tests removed, as requested in
#7350 (comment) .

I do urge you to reconsider and merge something like #7350 (including
the tests I wrote) instead. Without tests, I suspect this code will
break like its previous version did
. Once the code does break, it might be difficult to fix without tests.

Even if other parts of the theme work without tests, and even if you aren't in love with
how I set up the infrastructure in #7350 or #7338, I think this logic is complex enough
to need tests to be maintainable. Again, I wouldn't be able to check this code's correctness
without the tests that aren't included in this PR. You can always change
the infrastructure to something you like better later.

Of course, this is your project to maintain, so do what works best for you. If
this is the version that's most helpful to you, hope it helps!

---

Fixes #7226

Additionally, this allows using the version switcher even if the website
is published at a different URL than the site_url. In particular,
the version switcher should now work locally when serving the site with
mike serve.

[squidfunk]

Thanks for doing this!

To be clear, I did not say that we do not want tests, it's just the wrong time to start with it right now.

Two things: please change your filenameing convention to how we structured the rest of this repository – find a shorter name and put it into a directory, as the rest of the entire TypeScript codebase, something like corresponding-page/index.md, or shorter. The reason is that it's easier to put files alongside files, like .eslintrc and friends.

Additionally, please add a description to the functions, so that comments are complete, and please fix the remaining checks.

[ilyagr]

OK, done.

[squidfunk]

Thanks, LGTM!