Cleanup and some code reuse between Device- and normal Plugins

Summary: Introducing a base abstract class (blegh) to share some life cycle management between Device- and normal plugins. Cleaned up the test utils a bit as well + some old TODO's that now have been taken care of

Reviewed By: nikoant

Differential Revision: D22727089

fbshipit-source-id: 507816f1bfdbc6e7e71d4bd365b881b6710ca917

desktop/app/src/dispatcher/plugins.tsx

@@ -277,7 +277,6 @@ const requirePluginInternal = (
 
   if (pluginDetails.flipperSDKVersion) {
     // Sandy plugin
-    // TODO: suppor device Plugins T68738317
     return new SandyPluginDefinition(pluginDetails, plugin);
   } else {
     // classic plugin