Suport device-open-app command

Summary: It is an escape hatch for testing iOS Sample app if `navigate('/')` cannot be made to work easily (D51394323)

Reviewed By: lblasa

Differential Revision: D51466697

fbshipit-source-id: fd6c2f37504807b4b634b85cb10e837523dadba8

desktop/flipper-server-core/src/devices/ServerDevice.tsx

@@ -82,4 +82,8 @@ export abstract class ServerDevice {
   async installApp(_appBundlePath: string): Promise<void> {
     throw new Error('installApp not implemented');
   }
+
+  async openApp(_name: string): Promise<void> {
+    throw new Error('openApp not implemented');
+  }
 }