Add the updated third party libraries to the migration docs

Author: dtdesign

docs/migration/wsc61/libraries.md

@@ -0,0 +1,28 @@
+# Migrating from WoltLab Suite 6.1 - Third Party Libraries
+
+## Symfony PHP Polyfills
+
+The Symfony Polyfill for PHP 8.5 was added.
+
+Refer to the documentation within the [symfony/polyfill](https://github.com/symfony/polyfill/) repository for details.
+
+## Valinor
+
+The Valinor library that is being used to validate request parameters has been updated from version 1.17.0 to 2.1.1.
+
+This upgrade contains breaking changes that affect the error handling in particular.
+If you do not handle Valinor’s errors directly then you’re most likely not affected by this.
+
+Refer to Valinor’s [upgrade documentation](https://valinor.cuyz.io/2.1/project/upgrading/#upgrade-from-1x-to-2x) for details.
+
+## scssphp
+
+scssphp was updated from version 1.13.0 to 2.0.1.
+
+This is a complete rewrite of the scssphp library aimed at better compliance with the specifications.
+For the most part you should not be affected unless you are using SCSS constructs that previously had undefined behavior or otherwise violated the specs.
+
+Unfortunately, this version has a severe performance regression that increases build times by as much as 3x.
+Despite this drawback we had to upgrade in order to add support for PHP 8.4.
+
+Refer to the release notes for [scssphp/scssphp](https://github.com/scssphp/scssphp/releases/tag/v2.0.0) for a list of all (breaking) changes.

mkdocs.yml

@@ -136,6 +136,7 @@ nav:
           - 'Templates': 'migration/wsc61/templates.md'
           - 'Quotes': 'migration/wsc61/quotes.md'
           - 'Caching': 'migration/wsc61/caching.md'
+          - 'Third Party Libraries': 'migration/wsc61/libraries.md'
       - 'From WoltLab Suite 6.0':
           - 'PHP API': 'migration/wsc60/php.md'
           - 'Templates': 'migration/wsc60/templates.md'