build/lib/builtInExtensions.ts/getExtensionStream
export function getExtensionStream(extension: IExtensionDefinition) {
	// if the extension exists on disk, use those files instead of downloading anew
	if (isUpToDate(extension)) {
		log('[extensions]', `${extension.name}@${extension.version} up to date`, ansiColors.green('✔︎'));
		return vfs.src(['**'], { cwd: getExtensionPath(extension), dot: true })
			.pipe(rename(p => p.dirname = `${extension.name}/${p.dirname}`));
	}

	return getExtensionDownloadStream(extension);
}