Add exec Node API to FlipperLib

Summary: Changelog: Allow flipper plugins to run "exec" Node API on Flipper server.

Reviewed By: mweststrate

Differential Revision: D32881149

fbshipit-source-id: 46486a47ee9824ca68897c19fd86b4afc7f8bf1d

desktop/flipper-plugin/src/test-utils/test-utils.tsx

@@ -389,6 +389,12 @@ export function createMockFlipperLib(options?: StartPluginOptions): FlipperLib {
       appPath: process.cwd(),
       homePath: `/dev/null`,
     },
+    removeNodeAPI: {
+      childProcess: {
+        exec: jest.fn(),
+      },
+      fs: {},
+    },
   };
 }