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 `getBodyParamSettings`
** remove `assertContentType` and move the expected content types to `getSupportedRequestTypes()`
** add `assertValidTopLevelTypes` check to `parseBodyData()`
** adjusts e2e tests according to the new expected responses
** see https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/1028919 and https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/1047481 for an example
* remove `TypeValidatingJsonBodyValidator`
* add application/json-patch+json to any PATCH endpoint e2e tests that are missing it, see e.g. `repo/rest-api/tests/mocha/api-testing/PatchPropertyStatementTest.js` once https://gerrit.wikimedia.org/r/c/mediawiki/core/+/1049848 is merged