src/vs/platform/extensionManagement/node/extensionsScanner.ts/ExtensionsScanner/devSystemExtensionsPath
class ExtensionsScanner:	private get devSystemExtensionsPath(): string {
		if (!this._devSystemExtensionsPath) {
			this._devSystemExtensionsPath = path.normalize(path.join(FileAccess.asFileUri('', require).fsPath, '..', '.build', 'builtInExtensions'));
		}
		return this._devSystemExtensionsPath;
	}