Add exec Node API to FlipperLib

Summary: Changelog: Allow flipper plugins to run "exec" Node API on Flipper server.

Reviewed By: mweststrate

Differential Revision: D32881149

fbshipit-source-id: 46486a47ee9824ca68897c19fd86b4afc7f8bf1d

desktop/flipper-ui-browser/src/flipperServerConnection.tsx

@@ -69,6 +69,7 @@ export function createFlipperServer(): Promise<FlipperServer> {
     });
 
     socket.on('exec-response-error', (id: number, error: any) => {
+      // TODO: Deserialize error
       console.debug('exec <<< [SERVER ERROR]', id, error);
       const entry = pendingRequests.get(id);
       if (!entry) {