Doc: Persist current page when switching versions

[geographika]

Follow-up to #13480 based on comment at #11812 (comment)

Update renderVersions function to persist current page when selecting versions at the bottom of the TOC.
Tested on https://geographika-gdal.readthedocs.io/ (it can only be tested on a RTD deployment, not locally).

I've also opened a PR upstream with these changes: readthedocs/sphinx_rtd_theme#1663

cc @dbaston

[rouault]

Neat.

What happens if the sub-page doesn't exist in the branch we switch to ? 404 error ? Is there a way to avoid that and just go to the root page of the new branch ?

[dbaston]

What happens if the sub-page doesn't exist in the branch we switch to ? 404 error ?

I get a 404, which isn't terrible.

Is there a way to avoid that and just go to the root page of the new branch ?

I guess we'd need to add some redirects.