feat(action-button): S2 migration

[cdransf]

Description

Umbrella PR for the swc-action-button 1st-gen → 2nd-gen Spectrum 2 migration. All phase PRs target this branch and are merged here before this PR lands on main.

Migration plan: CONTRIBUTOR-DOCS/03_project-planning/03_components/action-button/migration-plan.md (merged in #6327)

Phase PRs

Phase	PR	Status
Phase 2 — Structure	#6339	Done
Phase 3 — API	#6339	Done
Phase 4 — Accessibility	#6348	Open
Phase 5 — Styling	—	Not started
Phase 6 — Testing	—	Not started
Phase 7 — Documentation	—	Not started

Reviewers: individual phase PRs are the right place for line-level review. This PR is for final integration sign-off.

Motivation and context

swc-action-button is part of the Spectrum 2 component migration workstream. Key changes from 1st-gen:

• Renders an internal native <button> as the semantic control (host no longer carries role="button")
• Removes toggles, selected, emphasized — toggle UX moves to swc-toggle-button / swc-toggle-button-group
• Defers hold-affordance / longpress
• Removes the link API (href and related attributes)
• accessible-label replaces label; aria-haspopup / aria-expanded are forwarded to the inner <button> for menu-trigger patterns
• Adds pending state (new in 2nd-gen, matching swc-button)
• Exposes a small reviewed set of --swc-action-button-* custom properties instead of the 1st-gen --mod-* / --spectrum-actionbutton-* chain

Related issue(s)

SWC-2039

Author's checklist

• I have read the CONTRIBUTING and PULL_REQUESTS documents.
• I have reviewed the Accessibility Practices for this feature, see: Aria Practices
• I have added automated tests to cover my changes.
• I have included a well-written changeset if my change needs to be published.
• I have included updated documentation if my change required it.

Reviewer's checklist

• Includes a Github Issue with appropriate flag or Jira ticket number without a link
• Includes thoughtfully written changeset if changes suggested include patch, minor, or major features
• Automated tests cover all use cases and follow best practices for writing
• Validated on all supported browsers
• All VRTs are approved before the author can update Golden Hash

Manual review test cases

To be populated in Phase 6 (testing). See the migration plan for the full verification matrix.

Device review

• Did it pass in Desktop?
• Did it pass in (emulated) Mobile?
• Did it pass in (emulated) iPad?

Accessibility testing checklist

To be populated in Phase 6 (testing). See the migration plan accessibility verification section for the full checklist.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 578f5dd

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[github-actions]

📚 Branch Preview Links

• Documentation Site (first-gen)
• Storybook (first-gen)
• Storybook (second-gen)

🔍 First Generation Visual Regression Test Results

When a visual regression test fails (or has previously failed while working on this branch), its results can be found in the following URLs:

• Spectrum | Light | Medium | LTR
• Spectrum | Dark | Large | RTL
• Express | Light | Medium | LTR
• Express | Dark | Large | RTL
• Spectrum-two | Light | Medium | LTR
• Spectrum-two | Dark | Large | RTL
• High Contrast Mode | Medium | LTR

Deployed to Azure Blob Storage: pr-6340

If the changes are expected, update the current_golden_images_cache hash in the circleci config to accept the new images. Instructions are included in that file.
If the changes are unexpected, you can investigate the cause of the differences and update the code accordingly.