Improve admin UI accessibility

[murshed]

Enhance accessibility throughout the plugin check admin interface:

• Add screen reader announcements for check status (starting, success, errors)
• Improve CSS for screen-reader-text with clip-path and white-space
• Use semantic HTML: convert table header to
• Fix legend text to display labels instead of IDs for better context
• Correct escaping functions: esc_html_e() instead of esc_attr_e() for headings
• Use textContent instead of innerText in JS for better practice
• Add wp-a11y dependency for ARIA live regions
• Remove duplicate spinner element
• Improve html_entity_decode() with proper flags

What?

This PR improves accessibility (WCAG compliance), HTML standards, screen reader notifications, and PHP 8+ compatibility across the Plugin Check admin UI and core libraries.

Why?

• Screen reader users were not receiving ARIA live region updates when checks were started, completed, or failed.
• Form controls contained duplicate IDs (#plugin-check__spinner), unlocalized raw slug text in <legend> tags, and incorrect escaping functions (esc_attr_e() instead of esc_html_e()).
• Table header rows in <thead> used non-semantic <td> cells rather than <th scope="col"> cells.
• Offscreen screen-reader CSS relied on outdated clip properties without modern clip-path: inset(50%) and white-space: nowrap.
• JS DOM manipulation used innerText instead of textContent, causing unnecessary browser style recalculations and reflows.
• html_entity_decode() in Parser.php was missing explicit $flags, triggering PHP 8.1+ default parameter deprecation issues.

How?

1. PHP 8+ Compatibility: Added ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML401 flags to html_entity_decode() in includes/Lib/Readme/Parser.php.
2. HTML & Escaping:
   • Removed the duplicate plugin-check__spinner element in templates/admin-page.php.
   • Updated section headings inside <h4> tags to use esc_html_e().
   • Changed fieldset <legend> screen-reader text to display human-readable labels ($label) instead of raw slugs.
   • Converted <thead> cells from <td> to <th scope="col"> in templates/results-table.php.
3. JS & ARIA Live Announcements:
   • Added 'wp-a11y' dependency to plugin-check-admin script registration in includes/Admin/Admin_Page.php.
   • Integrated wp.a11y.speak() notifications in assets/js/plugin-check-admin.js for check startup, execution summary, and error reporting.
   • Replaced innerText = '' with textContent = '' for clearing results containers.
4. CSS Improvements: Modernized offscreen screen-reader hiding rules in assets/css/plugin-check-admin.css with clip-path: inset(50%) and white-space: nowrap.

Testing Instructions

1. Navigate to Tools > Plugin Check.
2. Run a check on any installed plugin.
3. Verify with a screen reader (e.g. VoiceOver, NVDA) that announcements are spoken when checks start ("Running plugin checks…") and when checks complete with results.
4. Inspect the results table markup to ensure <thead> cells use <th scope="col">.
5. Verify HTML validation: check that no duplicate #plugin-check__spinner IDs exist on the page.
6. Run vendor/bin/phpcs --standard=PHPCompatibility --runtime-set testVersion 8.0-8.5 and verify 0 compatibility errors.
7. Run vendor/bin/phpcs and vendor/bin/phpstan analyse to verify linting and static analysis pass cleanly.

AI Usage Disclosure

• This PR was created without the help of AI tools
• This PR includes AI-assisted code or content

If AI tools were used, please describe how they were used:
Used AI coding agent to perform static analysis auditing for PHP 8+ compatibility, WCAG accessibility standards adherence, and automated linting verification.

Screenshots or screencast

Before	After
N/A	N/A

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Co-authored-by: murshed <fahimmurshed@git.wordpress.org>

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