Adds an Accessibilty Checker to the WordPress page/post preview. The checker identifies potential accessibility issues and provides guidance on host to improve.

• Augmented content preview with accessibility analysis and tips.
• Extended block editor core image element, to include decorative image toggle.
• A new page in Media admin area with editable fields for default media element alt attributes and their decorative flags.
• Optional augmented content filtering to ensure default alt attributes text gets added to legacy images (see Settings > Accessibility).

See scripts section in package.json