feat(sidebar): add collapsible root sidebar groups

[sy-records]

Summary

Related issue, if any:

Fixes #900

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

For any code change,

• Related documentation has been updated, if needed
• Related tests have been added or updated, if needed

Does this PR introduce a breaking change?

• Yes
• No

Tested in the following browsers:

• Chrome
• Firefox
• Safari
• Edge

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[paulhibbitts]

Thanks for taking this long-requested feature on @sy-records !

Here is my test sandbox:
https://codesandbox.io/p/devbox/vibrant-brattain-hj7935

I am concerned that the introduction of using bold to mark new expandable/collapsible sections might be confusing for users and add visual complexity to the sidebar.

One alternative would be to use the existing Chevron indicators to show expandable/collapsible sections (with existing rotation behavior), and do so without little additional visual complexity. Here is a quick mockup:

What do you think?

[paulhibbitts]

You might also find this closed issue a helpful reference @sy-records : #1564

I am not suggesting additional functionality at this point, but the comment by jhildenbiddle was also quite insightful for future consideration re: initial expaned/collapsed state.

[sy-records]

The bold text represents the original logic; now it simply supports clicking to expand or collapse it and marks its status so you don’t have to click repeatedly when viewing it.

Using a V-shaped indicator will change the current style.

[paulhibbitts]

I am not sure I follow, if bold text is used, and is also in multiple locations, this will likely be confusing for users re: cue of feedback. If I understand correctly possible, I suggest we use the established chevon feedback which is also used by other similar sidebar navs like Docusaurus https://docusaurus.io/docs/category/guides.

If bold is only possible I suggest setting aside this feature as the downsides would outweigh the possible upsides to me.

[sy-records]

I added logic to the sidebar-chevron.