Introduce menu entry support

Summary:
[interesting] since it shows how Flipper APIs are exposed through sandy. However, the next diff is a much simpler example of that

This diff adds support for adding menu entries for sandy plugin (renamed keyboard actions to menus, as it always creates a menu entry, but not necessarily a keyboard shortcut)

```

  client.addMenuEntry(
    // custom entry
    {
      label: 'Reset Selection',
      topLevelMenu: 'Edit',
      handler: () => {
        selectedID.set(null);
      },
    },
    // based on built-in action (sets standard label, shortcut)
    {
      action: 'createPaste',
      handler: () => {
        console.log('creating paste');
      },
    },
  );
```

Most of this diff is introducing the concept of FlipperUtils, a set of static Flipper methods (not related to a device or client) that can be used from Sandy. This will for example be used to implement things as `createPaste` as well

Reviewed By: nikoant

Differential Revision: D22766990

fbshipit-source-id: ce90af3b700e6c3d9a779a3bab4673ba356f3933

desktop/app/src/init.tsx

@@ -10,6 +10,7 @@
 import {Provider} from 'react-redux';
 import ReactDOM from 'react-dom';
 import {useState, useEffect} from 'react';
+
 import ContextMenuProvider from './ui/components/ContextMenuProvider';
 import GK from './fb-stubs/GK';
 import {init as initLogger} from './fb-stubs/Logger';
@@ -36,6 +37,7 @@ import {enableMapSet} from 'immer';
 import os from 'os';
 import QuickPerformanceLogger, {FLIPPER_QPL_EVENTS} from './fb-stubs/QPL';
 import {PopoverProvider} from './ui/components/PopoverProvider';
+import {initializeFlipperLibImplementation} from './utils/flipperLibImplementation';
 
 if (process.env.NODE_ENV === 'development' && os.platform() === 'darwin') {
   // By default Node.JS has its internal certificate storage and doesn't use
@@ -111,6 +113,7 @@ function setProcessState(store: Store) {
 }
 
 function init() {
+  initializeFlipperLibImplementation(store, logger);
   ReactDOM.render(<AppFrame />, document.getElementById('root'));
   initLauncherHooks(config(), store);
   const sessionId = store.getState().application.sessionId;