src/vs/workbench/services/languageDetection/browser/languageDetectionWorkerServiceImpl.ts/LanguageDetectionService/getLanguageId
class LanguageDetectionService:	private getLanguageId(language: string | undefined): string | undefined {
		if (!language) {
			return undefined;
		}
		if (this._languageService.isRegisteredLanguageId(language)) {
			return language;
		}
		return this._languageService.guessLanguageIdByFilepathOrFirstLine(URI.file(`file.${language}`)) ?? undefined;
	}