src/vs/workbench/services/languageDetection/browser/languageDetectionWorkerServiceImpl.ts/LanguageDetectionWorkerClient/getLanguageId
class LanguageDetectionWorkerClient:	getLanguageId(languageIdOrExt: string | undefined) {
		if (!languageIdOrExt) {
			return undefined;
		}
		if (this._languageService.isRegisteredLanguageId(languageIdOrExt)) {
			return languageIdOrExt;
		}
		const guessed = this._guessLanguageIdByUri(URI.file(`file.${languageIdOrExt}`));
		if (!guessed || guessed === 'unknown') {
			return undefined;
		}
		return guessed;
	}