Motivation
Migration to context-based DI aims to separate creation from logic. Using Parser::__constructor (new Parser) demands to support backward compatibility.
At the moment Parser already uses DI, but a lot of legacy code in extension creates it directly via constructor.
https://codesearch.wmflabs.org/search/?q=new%20%5C%5C%3FParser%5C(&i=nope&files=&repos=
Expected Result:
All occurrences of new Parser() should be replaced in favor of creating it via factory (both core and extensions):
MediaWikiServices::getInstance()->getParserFactory()->create();