src/vs/workbench/services/extensions/electron-browser/cachedExtensionScanner.ts/getExtraDevSystemExtensionsRoot
function getExtraDevSystemExtensionsRoot(): string {
	if (!_ExtraDevSystemExtensionsRoot) {
		_ExtraDevSystemExtensionsRoot = path.normalize(path.join(FileAccess.asFileUri('', require).fsPath, '..', '.build', 'builtInExtensions'));
	}
	return _ExtraDevSystemExtensionsRoot;
}