extensions/typescript-language-features/src/typeScriptServiceClientHost.ts/TypeScriptServiceClientHost/getAllModeIds
class TypeScriptServiceClientHost:	private getAllModeIds(descriptions: LanguageDescription[], pluginManager: PluginManager) {
		const allModeIds = flatten([
			...descriptions.map(x => x.modeIds),
			...pluginManager.plugins.map(x => x.languages)
		]);
		return allModeIds;
	}