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/flipper-plugin/src/plugin/Plugin.tsx

@@ -9,6 +9,7 @@
 
 import {SandyPluginDefinition} from './SandyPluginDefinition';
 import {BasePluginInstance, BasePluginClient} from './PluginBase';
+import {FlipperLib} from './FlipperLib';
 
 type EventsContract = Record<string, any>;
 type MethodsContract = Record<string, (params: any) => Promise<any>>;
@@ -96,11 +97,12 @@ export class SandyPluginInstance extends BasePluginInstance {
   connected = false;
 
   constructor(
-    realClient: RealFlipperClient,
+    flipperLib: FlipperLib,
     definition: SandyPluginDefinition,
+    realClient: RealFlipperClient,
     initialStates?: Record<string, any>,
   ) {
-    super(definition, initialStates);
+    super(flipperLib, definition, initialStates);
     this.realClient = realClient;
     this.definition = definition;
     this.client = {