Sidebar categories don't autocollapse when navigating via paginator

[pranabdas]

Have you read the Contributing Guidelines on issues?

• I have read the Contributing Guidelines on issues.

Motivation

When autoCollapseCategories is set to true, I think it would be consistent to collapse all the non-current sidebar categories leaving only one actively open category. This is what happens when we open a new sidebar category by clicking on the sidebar. However, if we trigger open a new category via PaginatorNavLink button, it does not trigger collapse for the previously opened categories.

For example, let's open https://docusaurus.io/docs/typescript-support, which is the last page of Getting Started category. Now clicking on the next category i.e., Guides in the sidebar would collapse the Getting Started and open Guides. Now, go back to previous page, scroll down to the bottom of the page, and click the Next button, it will open Guides category in the sidebar but also leave the Getting Started open.

Self-service

• I'd be willing to do some initial work on this proposal myself.

[Josh-Cena]

It's a bug. We should always leave only one category open.

The entire logic around this is a bit messy. I don't even fully know what's going on...