This allows other extensions to use this too, without needing a hack to detect
ULS's existence and work around it by not loading their copies of j/i18n code.
Preserves backwards-compatibility for archaïc versions of MediaWiki.
Bug: T95666
Change-Id: I25b33437ceddb60570322b9aa51844acc42a3e32
Retaining the UniversalLanguageSelector.php and Resources.php
to avoid breaking support for old MW versions. At some point,
we can validate how many old MW versions we need to support.
Bug: T87987
Change-Id: I006e968b70298b54013177aa792a4dfdf5b6aae2