Spawned off of T138738 to reduce confusion around the meaning of wikibase-related config variables.
- wgMFUseWikibaseDescription -> wgMFUseWikibase
- Fold wgMFDisplayWikibaseDescription and wgMFDisplayWikibaseDescriptionsAsTaglines into new wgMFDisplayWikibaseDescriptions, changing it from a boolean to an object describing which features on which to display descriptions
- Deprecation of wgMFUseWikibaseDescription and wgMFDisplayWikibaseDescription
[ ] Corresponding variables changed in mediawiki-config as well (To be done in follow-up task when variables are fully deprecated)