chore(icons): centralize rtl handling for icons in swc-ui-icon

[cdransf]

Description

Moves chevron/arrow RTL mirroring into <swc-ui-icon> itself (new ui-icon-direction.css, curated chevron/arrow list, icon now reflect: true). Removes accordion-item.css's now-redundant mirror rule (kept its RTL+open rotation compensation, which is genuinely Accordion-specific). Adds 5 tests covering direct + inherited dir, both curated icons, and non-directional exclusion. Note: :host(:dir(rtl))[icon="x"] silently fails to match in Chromium; both conditions must be inside :host()'s own argument (:host(:dir(rtl)[icon="x"])), documented in the CSS.

Motivation and context

RFC icon-rfc.md section 11 (resolved): mirror directional UI icons via :dir(rtl) in the UI icon stylesheet, owned by <swc-ui-icon>, not components.

Related issue(s)

• Jira: SWC-2440

Screenshots (if appropriate)

None. Accordion's VRT snapshot (covers RTL) is byte-identical before/after.

Author's checklist

• I have read the CONTRIBUTING and PULL_REQUESTS documents.
• I have reviewed the Accessibility Practices for this feature.
• 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

• Storybook, any component with a chevron/arrow swc-ui-icon (e.g. Accordion): flip page dir to rtl, confirm it mirrors; flip back, confirm it un-mirrors.
• Confirm a non-directional icon (e.g. checkmark) never mirrors under RTL.

Device review

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

Accessibility testing checklist

• Keyboard: N/A, visual-only change, no new interactive elements.
• Screen reader: N/A. IconBase's existing host-owned a11y (decorative by default, role="img" when labeled) is untouched; the icon's own inner SVG was already never announced.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 9447838

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

• Storybook (Gen2, dev mode)
• Storybook (Gen2, prod mode)
• Documentation Site (Gen1)
• Storybook (Gen1)

🔍 Gen1 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-6579

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.