Updates to compiled stylesheet

[rezrah]

Summary

Addresses multiple issues in the compiled stylesheet, including:

• Removal of escaped characters in selectors where modern CSS features like :has are used
• Switched to use CSS Logical Properties in compiled output, which is both necessary to fix the above and is now worth doing as the feature is widely available in modern browsers.

Compiled CSS output size is now 9% lower than before.

Fixes #823

List of notable changes:

• Updates relevant postcss dependency in order to prevent rewriting of :has selectors. Previous versions are deprecated, so an upgrade was needed.
• Adds rule to preserve source usage of :has and logical properties

What should reviewers focus on?

• Diff the current production bundle with the canary equivalent

Steps to test:

1. Copy this (current) and enter into left hand side of a diff checker
2. Copy this (canary) and enter into right hand side of a diff checker
3. Manually compare the output and verify that only changes are:

• direct use of logical properties
• escaped chars have been removed
• some other legacy rules have been removed, but nothing that is relevant to modern browsers

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:

Before	After

[changeset-bot]

🦋 Changeset detected

Latest commit: 7430ffd

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	Minor
@primer/brand-primitives	Minor
@primer/brand-e2e	Minor
@primer/brand-fonts	Minor
@primer/brand-config	Minor
@primer/brand-storybook	Minor

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[github-actions]

🟢 No design token changes found

[github-actions]

🟢 No visual differences found

Our visual comparison tests did not find any differences in the UI.