SubNav v2 a11y fixes

[rezrah]

Summary

Follow up to #851

Fixes additional issues found during upgrade, but non-blocking for the latest dotcom upgrade release.

List of notable changes:

• Removed focus-trapping in the menu overlay on narrow viewports
• Added hover state to the SubNav.Heading
• Added aria-current visual indicator parity on narrow viewports in mobile overlay
• Separator now shows by default even if aria-current isn't set, but hidden on mobile

What should reviewers focus on?

• Verify fixes work as expected and are not introducing any other regressions

Contributor checklist:

• All new and existing CI checks pass
• Tests prove that the feature works and covers both happy and unhappy paths
• Any drop in coverage, breaking changes or regressions have been documented above
• UI Changes contain new visual snapshots (generated by adding update snapshots label to the PR)
• All developer debugging and non-functional logging has been removed
• Related issues have been referenced in the PR description

Reviewer checklist:

• Check that pull request and proposed changes adhere to our contribution guidelines and code of conduct
• Check that tests prove the feature works and covers both happy and unhappy paths
• Check that there aren't other open Pull Requests for the same update/change

Screenshots:

Please try to provide before and after screenshots or videos

Removed focus trapping:

Before	After
Screen.Recording.2024-12-09.at.15.45.54.mov	Screen.Recording.2024-12-09.at.15.46.21.mov

Separator by default:

Before	After

[changeset-bot]

🦋 Changeset detected

Latest commit: d1c1579

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

This PR includes changesets to release 6 packages

Name	Type
@primer/react-brand	Patch
@primer/brand-primitives	Patch
@primer/brand-e2e	Patch
@primer/brand-fonts	Patch
@primer/brand-config	Patch
@primer/brand-storybook	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

🟢 No design token changes found

[github-actions]

⚠️ Visual differences found

Our visual comparison tests found UI differences.

Please review the differences by using the test artifacts to ensure that the changes were intentional.

Artifacts can be downloaded and reviewed locally.

Download links are available at the bottom of the workflow summary screen.

Example:

If the changes are expected, please run npm run test:visual:update-snapshots to replace the previous fixtures.

Review visual differences

[stamat]

Just tested it! Looking 👌 perfect! Removing the focus trap solves the issue of accessing the close button and closing the subnav on focus out. We can reintroduce the focus trap once we take a deeper look into the focus trap we import from gh behaviors or primer... I forgot...

[danielguillan]

Works great!