Some renames

Summary:
Some non-semantic changes. Mostly an earlier rename that was accidentally done only locally rather than across the codebase

Also support `.spec` test extension, which is more idiomatic Jest, since we don't use the `.node` and `.electron` distinction anymore anyway.

Reviewed By: jknoxville

Differential Revision: D22976438

fbshipit-source-id: f3abedb36cbac1e835295177117ccbca492a67a1

desktop/app/src/utils/__tests__/messageQueueSandy.node.tsx

@@ -23,7 +23,7 @@ import {registerPlugins} from '../../reducers/plugins';
 import {
   SandyPluginDefinition,
   TestUtils,
-  FlipperClient,
+  PluginClient,
   SandyPluginInstance,
 } from 'flipper-plugin';
 
@@ -33,7 +33,7 @@ type Events = {
   };
 };
 
-function plugin(client: FlipperClient<Events, {}>) {
+function plugin(client: PluginClient<Events, {}>) {
   const state = {
     count: 0,
   };