implementations of ContentHandler::fillParserOutput MUST set HTML if
$cpoParams->getGenerateHtml() returns true.
Bug: T321319
Change-Id: Ibd43f7420e949666649752dce7072dc35bc1f440
When invalid JSON is being saved, change the error message from the
generic "invalid-content-data" to "invalid-json-data" with the specific
error passed as param.
Allow extensions to hook into JSON validation, enabling them to apply
additional validations for specific JSON files such as MediaWiki:*.json
config files. The page identity is passed to the hook.
Bug: T313254
Change-Id: If9590c29ed0b871b03a3db8f13e72ee9cfdd7e2b