Security Audit & Remediation: manual-emulator-testing (#467)

* Update dependencies, engine requirements, fix index.html syntax, and add local package-lock.json for manual-emulator-testing

* Fix user object handling, remove redundant setUser calls, and prevent duplicate snapshot listeners

Author: inlined

manual-emulator-testing/README.md

@@ -1,7 +1,7 @@
 # Manual testing using the Emulator Suite
 
 This directory contains a very basic web app that connects to the
-Cloud Firestore and Firebase Authentication emulators. 
+Cloud Firestore and Firebase Authentication emulators.
 
 You sign in and read and write data in a completely local environment.
 
@@ -15,10 +15,10 @@ You will also need the [Firebase CLI](https://firebase.google.com/docs/cli).
 First start the emulators:
 
 ```
-firebase --project=fakeproject emulators:start 
+firebase --project=fakeproject emulators:start
 ```
 
-Next visit `http://localhost:5000` in your browser and you should see a 
-_very_ barebones chat app powered by the Cloud Firestore and Firebase 
+Next visit `http://localhost:5000` in your browser and you should see a
+_very_ barebones chat app powered by the Cloud Firestore and Firebase
 Authentication emulators. Try adding some messages and then click the link
 at the bottom of the UI to view the messages in the Emulator UI.

manual-emulator-testing/firebase.json

@@ -5,11 +5,7 @@
   },
   "hosting": {
     "public": "public",
-    "ignore": [
-      "firebase.json",
-      "**/.*",
-      "**/node_modules/**"
-    ],
+    "ignore": ["firebase.json", "**/.*", "**/node_modules/**"],
     "rewrites": [
       {
         "source": "**",