The feature manager abstracts away how a feature is enabled from the
consumer of that feature. Accordingly, replace direct instantiation of
SkinVersionLookup with usage of the Vector.FeatureManager service.
Supporting changes:
- Add Vector\VectorServices, a simple wrapper around
MediaWiki\MediaWikiServices that allows us to both document and
type-hint services specific to Vector
- Add Vector\Hooks::isSkinVersionLegacy to minimise repetition
Additional changes:
- Make the MakeGlobalVariablesScript hook handler return early if the
user isn't using the Vector skin like the other hook handlers
Bug: T256100
Change-Id: I93b5ef39802323c7ac658af8fa7cc312fff68aa7
