[Sync EN] `FILTER_VALIDATE_DOMAIN`: document acceptance of arbitrary characters (#5867)

[github-actions]

Commit: https://github.com/php/doc-en/commit/74492d20fff2f42c8aef4ba02f4bf4b59e2f8fcc
PR: https://github.com/php/doc-en/pull/5867

Nouveaux fichiers EN (pas encore traduits)

• reference/filter/constants.validation.xml