Add --launcher-msg option to pass to desktop app

Summary:
Allows the launcher to provide messages to the user. Currently, in the form
of the red notification bar at the bottom. This is just meant as a temporary measure
during the alpha to have some clearly noticeable way of getting the user's attention.

I consider removing this a blocker for the release as this mechanism is not well
suited for this in many ways.

The current use case for this is providing a warning if a cached version is used
instead of the requested one, e.g. "Could not fetch requested Flipper version 'deadbeef', using cached version instead."

Reviewed By: jknoxville, priteshrnandgaonkar

Differential Revision: D14073687

fbshipit-source-id: 85630347027063103315eeb1286731fe2478e261

src/utils/launcher.js

@@ -0,0 +1,19 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+
+import type {ProcessConfig} from './processConfig.js';
+import type {Store} from '../reducers/index.js';
+
+export function initLauncherHooks(config: ProcessConfig, store: Store) {
+  // TODO(T40488739): This must be replaced with a proper display before launching this.
+  if (config.launcherMsg) {
+    store.dispatch({
+      type: 'SERVER_ERROR',
+      payload: config.launcherMsg,
+    });
+  }
+}