Composer: Add ezyang/htmlpurifier for ILIAS 12

[fhelfer]

This PR suggests adding ezyang/htmlpurifier (v. 4.19) as composer dependency.

General Information:

• this dependency was already used in ILIAS.
• License: LGPL-2.1

Usage:

• components/ILIAS/Html

Wrapped By:

• \ilHtmlPurifierAbstractLibWrapper (implements \ilHtmlPurifierInterface)

Reasoning:

• HTMLPurifier is a standards-compliant HTML filter library written in PHP. It will not only remove all malicious code (better known as XSS) with a thoroughly audited, secure yet permissive whitelist, it will also make sure your documents are standards compliant, something only achievable with a comprehensive knowledge of W3C's specifications.
• We should not try to/do not want to reinvent the wheel in ILIAS and rely on this security library when filtering HTML code.

Maintenance:

• HTMLPurifier is actively maintained by multiple contributors. There is recent activity (1 month ago, see: https://github.com/ezyang/htmlpurifier/commits/master).
• Security issues are always fixed in a timely manner followed by new releases. Similar to ILIAS the project provides a mailing list for security advisories: http://htmlpurifier.org/contact .

Alternatives:

• https://github.com/symfony/html-sanitizer

Links:

• Packagist: https://packagist.org/packages/ezyang/htmlpurifier
• GitHub: https://github.com/ezyang/htmlpurifier
• Documentation: http://htmlpurifier.org/docs

[matthiaskunkel]

Jour Fixe, 08 DEC 2025: Dependency is accepted for ILIAS 12.

[lscharmer]

Merged with PR: #11255