Read flipper-plugin from peer deps

Summary:
To know whether plugins should be mounted with the old setup or new setup (with a Provided / context based api), we need to be able to recognize whether a plugin is written with the old or new setup.

We do this by checking if the flipper-plugin dependency is declared as peer dependency. This we can to check for SDK compatibility as well.

Reviewed By: jknoxville

Differential Revision: D22043085

fbshipit-source-id: 21afabb6e58d86253a464470f4690c51cced87ab

desktop/plugin-lib/src/PluginDetails.ts

@@ -26,4 +26,5 @@ export default interface PluginDetails {
     email?: string;
     url?: string;
   };
+  flipperSDKVersion?: string;
 }