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/Client.tsx

@@ -40,6 +40,7 @@ import {debounce} from 'lodash';
 import {batch} from 'react-redux';
 import {SandyPluginInstance} from 'flipper-plugin';
 import {flipperMessagesClientPlugin} from './utils/self-inspection/plugins/FlipperMessagesClientPlugin';
+import {getFlipperLibImplementation} from './utils/flipperLibImplementation';
 
 type Plugins = Array<string>;
 
@@ -310,7 +311,12 @@ export default class Client extends EventEmitter {
         // TODO: needs to be wrapped in error tracking T68955280
         this.sandyPluginStates.set(
           plugin.id,
-          new SandyPluginInstance(this, plugin, initialStates[pluginId]),
+          new SandyPluginInstance(
+            getFlipperLibImplementation(),
+            plugin,
+            this,
+            initialStates[pluginId],
+          ),
         );
       }
     });
@@ -355,7 +361,7 @@ export default class Client extends EventEmitter {
       // TODO: needs to be wrapped in error tracking T68955280
       this.sandyPluginStates.set(
         plugin.id,
-        new SandyPluginInstance(this, plugin),
+        new SandyPluginInstance(getFlipperLibImplementation(), plugin, this),
       );
     }
   }