Add expand to NavList

[TylerJDev]

Adds new component NavList.ShowMoreItem, allows native support for "expanding" content within a NavList.

Closes https://github.com/github/primer/issues/2637

Proposed API

Basic example:

export const WithExpand = () => {
  const items = [
    {href: '#', text: 'Item 4'},
    {href: '#', text: 'Item 5'},
    {href: '#', text: 'Item 6'},
    {href: '#', text: 'Item 7'},
    {href: '#', text: 'Item 8'},
    {href: '#', text: 'Item 9'},
  ]

  return (
    <NavList>
      <NavList.Item href="#" aria-current="page">
        Item 1
      </NavList.Item>
      <NavList.Item href="#">Item 2</NavList.Item>
      <NavList.Item href="#">Item 3</NavList.Item>
      <NavList.GroupExpand label="Show more" items={items} />
    </NavList>
  )
}

Multiple expands:

export const ExpandWithPages = () => {
  const items = [
    {href: '#', text: 'Item 4'},
    {href: '#', text: 'Item 5'},
    {href: '#', text: 'Item 6'},
    {href: '#', text: 'Item 7'},
    {href: '#', text: 'Item 8'},
    {href: '#', text: 'Item 9'},
  ]

  return (
    <NavList>
      <NavList.Item href="#" aria-current="page">
        Item 1
      </NavList.Item>
      <NavList.Item href="#">Item 2</NavList.Item>
      <NavList.Item href="#">Item 3</NavList.Item>
      <NavList.GroupExpand pages={2} label="Show more" items={items} />
    </NavList>
  )
}

Group example (storybook)

Changelog

New

• Adds new component NavList.ShowMoreItem

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Testing & Reviewing

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: d22f63f

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

This PR includes changesets to release 1 package

Name	Type
@primer/react	Minor

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[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	106.02 KB (+0.24% 🔺)
packages/react/dist/browser.umd.js	106.33 KB (+0.15% 🔺)

[joshblack]

Congrats on putting this together! Just left a comment but approving since it's non-blocking 👍

[primer-integration]

👋 Hi from github/github! Your integration PR is ready: https://github.com/github/github/pull/363691

[primer-integration]

🟢 golden-jobs completed with status success.

[github-actions]

👋 Hi, there are new commits since the last successful integration test. We recommend running the integration workflow once more, unless you are sure the new changes do not affect github/github. Thanks!