Update Symfony link description for clarity [skip ci]

Update Drupal link to point to the correct homepage

Fix some links

Clean white list

Fix broken links

Add Url highlight library

Replace old PSR-7 middlewares with new PSR-15 middlewares

Replace Symfony Security Monitoring

Added PhpEd (IDE) & TCPDF (PDF generator)

Added TYPO3 CMS

Update README.md

Removed spress from static site generators, bad URL

* simplify guidelines

* tweak

* tweak

* tweak

* tweak

* tweak

* tweak

* tweak

* tweaks

Repo: https://github.com/Yoast/PHPUnit-Polyfills/
Packagist: https://packagist.org/packages/yoast/phpunit-polyfills

Full disclosure: I'm the maintainer of the package. Yes, I did read the contributing guide, so I'll make my case ;-)

* Used by > [35K dependents](https://github.com/Yoast/PHPUnit-Polyfills/network/dependents)
* Over [20M downloads via Packagist](https://packagist.org/packages/yoast/phpunit-polyfills/stats)
* Used by [popular packages on the list](https://packagist.org/packages/yoast/phpunit-polyfills/dependents?order_by=downloads), including WordPress.
* [Recommended by the author of PHPUnit itself](https://phpunit.de/supported-versions.html) for running tests on multiple PHPUnit versions.

Co-authored-by: jrfnl <jrfnl@users.noreply.github.com>

Update phpDocumentor info

Update link for PHP_CodeSniffer

PHP_CodeSniffer is under new management since December last year.
See: https://github.com/squizlabs/PHP_CodeSniffer/issues/3932

The package is now maintained in the https://github.com/PHPCSStandards/PHP_CodeSniffer repo.

* Fix to use the official name.
* Remove the version reference. Version 3 was released four years ago.
* Point the link to the official website, not the GH repo.