build/lib/builtInExtensions.ts/getExtensionDownloadStream
function getExtensionDownloadStream(extension: IExtensionDefinition) {
	const galleryServiceUrl = productjson.extensionsGallery?.serviceUrl;
	return (galleryServiceUrl ? ext.fromMarketplace(galleryServiceUrl, extension) : ext.fromGithub(extension))
		.pipe(rename(p => p.dirname = `${extension.name}/${p.dirname}`));
}