feat(ActionList): Combine Item and LinkItem into unified Item component

[liuliu-dev]

Closes #5916

Combines ActionList.Item and ActionList.LinkItem into a single unified ActionList.Item component that automatically switches between button and link behavior based on props. Developers no longer need to choose between Item and LinkItem

Changes

• New unified API: ActionList.Item now supports both button and link functionality. Automatically uses link behavior when href, to, or link-related props are provided. Existing ActionList.Item usage continues to work unchanged
• Internal refactor:
  • Renamed original Item to BaseItem
  • New Item component routes to BaseItem or LinkItem based on props
  • Updated LinkItem to use BaseItem internally
• Documentation updates: Updated API docs to reflect the combined functionality
• Update snapshots: Updated snapshots because the component name changed from ActionList.LinkItem to ActionList.Item

Usage Examples

// Button behavior (default)
<ActionList.Item onSelect={handleSelect}>
  Button item
</ActionList.Item>

// Link behavior 
<ActionList.Item href="/dashboard">
  Link item
</ActionList.Item>

// React Router link 
<ActionList.Item to="/settings" as={Link}>
  Router link item
</ActionList.Item>

Rollout strategy

• Major release; if selected, include a written rollout or migration plan

Testing & Reviewing

Testing in github-ui: https://github.com/github/github-ui/pull/4026

[changeset-bot]

🦋 Changeset detected

Latest commit: 5dddb63

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

This PR includes changesets to release 2 packages

Name	Type
@primer/react	Major
@primer/styled-react	Major

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[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github depends on. If you are GitHub staff, we recommend testing these changes with github/github using the integration workflow. Thanks!

[liuliu-dev]

Testing completed, closing this PR and will build a more polished implementation