NavList add defaultOpen to NavList.Item

[gracepark]

Closes https://github.com/github/primer/issues/2512

This adds the defaultOpen prop to NavList.Item. We needed this because in the Docs sidebar needs the ability to have a NavList.SubNav default to open even without an aria-current in its nested levels like so:

Another pro is that this essentially resolves depending on client-side rendering of our sidebar.

A few notes about my changes:

• I named the prop defaultOpen to follow a similar pattern to TreeView's defaultExpanded. We're wondering if it'd be a little more accurate to name it something like initiallyOpen, defaultToOpen or openOnStart.
• I wanted to catch the possiblity of setting a defaultOpen on a NavList.Item without a NavList.SubNav. I was thinking it could throw an error instead, but I noticed below other checks like depth were using console.error, so I did the same.

Thank you for the review, and please let me know if there are any questions or concerns!

Screenshots

No real visual difference unless a defaultOpen is added to a NavList.Item with a NavList.SubNav. That is shown above in the changes I described.

Merge checklist

• Added/updated tests
• Added/updated documentation
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge

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[changeset-bot]

🦋 Changeset detected

Latest commit: ad2a14f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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@primer/react	Patch

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[github-actions]

size-limit report 📦

Path	Size
dist/browser.esm.js	104.65 KB (+0.07% 🔺)
dist/browser.umd.js	105.21 KB (+0.07% 🔺)

[siddharthkp]

LGTM!

[siddharthkp]

I named the prop defaultOpen to follow a similar pattern to TreeView's defaultExpanded. We're wondering if it'd be a little more accurate to name it something like initiallyOpen, defaultToOpen or openOnStart

You're completely right, but because the HTML API has keys like defaultValue and defaultChecked, it's pretty common to see the same in the React ecosystem (For example in these docs)

To keep the API familiar, we have kept the same convention for props that set the initial value in primer/react as well

[siddharthkp]

• Merged to next release: v35.29.0 Release tracking #3679