Make flipper messages generally available, remove self inspection infra structure

Summary:
Changelog: Flipper message debugging moved from a separate device to the console tab

This makes message debugging easier accessible, and in production (recently requested at GH). Also it clears up a lot of infra that was created just to make flipper a self recursive inspection device + a separate plugin. While fun, a hardcoded setup is just a bit more simpler (no exception rules and better static verification)

Reviewed By: nikoant

Differential Revision: D29487811

fbshipit-source-id: b412adc3ef5bd831001333443b432b6c0f934a5e

desktop/flipper-plugin/src/plugin/PluginContext.tsx

@@ -25,6 +25,13 @@ export function usePluginInstance():
   return pluginInstance;
 }
 
+export function usePluginInstanceMaybe():
+  | SandyPluginInstance
+  | SandyDevicePluginInstance
+  | undefined {
+  return useContext(SandyPluginContext);
+}
+
 export function usePlugin<
   Factory extends PluginFactory<any, any> | DevicePluginFactory,
 >(plugin: Factory): ReturnType<Factory> {