Describe the bug

All major browsers support highlighting with Text Fragments, which is the #:~:text=... bit in a URL:

https://www.sphinx-doc.org/en/master/usage/quickstart.html#:~:text=In%20Sphinx%20source

It highlights and scrolls to the first match on the page, which is extremely useful. It's used by Google Search to scroll to a particular part of the page, and by LLMs to link to a relevant bit of the page they got their answers from, which is super useful these days.

Annoyingly, Sphinx's sphinx_highlight.js always removes this text fragment from the URL, making sharing of the exact URL the user found impossible.

How to Reproduce

Go to

https://www.sphinx-doc.org/en/master/usage/quickstart.html#:~:text=In%20Sphinx%20source

Notice that the URL bar is immediately replaced with

https://www.sphinx-doc.org/en/master/usage/quickstart.html

instead of the original

https://www.sphinx-doc.org/en/master/usage/quickstart.html#:~:text=In%20Sphinx%20source

Presumably this is due to

which is run unconditionally from