src/vs/editor/common/services/languagesRegistry.ts/LanguagesRegistry/getMimeType
class LanguagesRegistry:	public getMimeType(languageId: string): string | null {
		if (!hasOwnProperty.call(this._languages, languageId)) {
			return null;
		}
		const language = this._languages[languageId];
		return (language.mimetypes[0] || null);
	}