Add headless option to dump on disconnect

Summary:
This adds an optional exit strategy that reacts to the client disconnecting rather than a `SIGINT` which can be used for integration tests.

`MiddlewareAPI` is a subset of `Store` and required to work here.

Annoyingly, it's not quite clear to me why this does not work as part of an event loop cycle and requires a `setTimeout`. This doesn't have any negative effects and works in the same way that the SIGINT interruption works, but it's a bit of an eyesore.

Reviewed By: danielbuechele

Differential Revision: D14622111

fbshipit-source-id: e2caca056e478428d977565dc9bc09eefca4230c

src/utils/exportData.js

@@ -5,7 +5,7 @@
  * @format
  */
 import {getInstance as getLogger} from '../fb-stubs/Logger';
-import type {Store} from '../reducers';
+import type {Store, MiddlewareAPI} from '../reducers';
 import type {DeviceExport} from '../devices/BaseDevice';
 import type {State as PluginStates} from '../reducers/pluginStates';
 import type {PluginNotification} from '../reducers/notifications.js';
@@ -183,7 +183,9 @@ export const processStore = async (
   return null;
 };
 
-export async function getStoreExport(store: Store): Promise<?ExportType> {
+export async function getStoreExport(
+  store: MiddlewareAPI,
+): Promise<?ExportType> {
   const state = store.getState();
   const {clients} = state.connections;
   const {pluginStates} = state;
@@ -234,7 +236,7 @@ export async function getStoreExport(store: Store): Promise<?ExportType> {
   );
 }
 
-export function exportStore(store: Store): Promise<string> {
+export function exportStore(store: MiddlewareAPI): Promise<string> {
   getLogger().track('usage', EXPORT_FLIPPER_TRACE_EVENT);
   return new Promise(async (resolve, reject) => {
     const storeExport = await getStoreExport(store);