Add group support to ActionMenu

[camertron]

What are you trying to accomplish?

This PR adds group support to ActionMenu. Groups are already supported by sister component NavList, as well as by the React version of ActionMenu.

Screenshots

Groups	Groups and items together

Integration

No changes necessary in production - I was able to work groups in without changing the component's public interface.

Risk Assessment

• Low risk the change is small, highly observable, and easily rolled back.
• Medium risk changes that are isolated, reduced in scope or could impact few users. The change will not impact library availability.
• High risk changes are those that could impact customers and SLOs, low or no test coverage, low observability, or slow to rollback.

Accessibility

• No new axe scan violation - This change does not introduce any new axe scan violations.

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Lookbook)
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge

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[changeset-bot]

🦋 Changeset detected

Latest commit: 568f2ad

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

This PR includes changesets to release 1 package

Name	Type
@primer/view-components	Minor

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[github-actions]

⚠️ Visual differences found

Our visual comparison tests found UI differences. Please review the differences by viewing the files changed tab to ensure that the changes were intentional.

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