As per T361995 JsonBodyValidator from Mediawiki REST API is discontinued in favor of a new mechanism (T358560)
Wikibase REST API should stop using the deprecated class.
Implementation notes:
- for each POST/PUT/PATCH/DELETE route handler
- remove getBodyValidator
- move any field definitions that were previously in getBodyValidator to getParamSettings
- move content type check into parseBodyData()
- be careful about the very "flexible" body field validation (T364440). Some type casts may be needed.
- adjusts e2e tests according to the new expected responses
- see https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/1028919 for an example
- remove TypeValidatingJsonBodyValidator