Stop stubbing $wgLang and $wgContLang. There are no major code paths which do not...

Stop stubbing $wgLang and $wgContLang.  There are no major code paths which do not call either $wgLang or $wgContLang at least once.  All index.php calls unstub $wgContLang from MediaWiki::parseTitle() except in the edgecase of viewing pages referenced only by "curid=123", and since those will end up calling OutputPage::output() they will eventually be unstubbed at some point as well.  All calls through load.php unstub $wgLang in ResourceLoaderContext::getLanguage() from ResouceLoader::respond() --> ResourceLoader::preloadModuleInfo().  All calls through api.php unstub $wgContLang in ApiResult::cleanUpUTF8() from ApiMain::printResult().