Added arfoundation.extensions github repo as automatically resolved dependency in the package manifest so that the developer does not have to include it manually by hand

Author: cs-util

Packages/manifest.json

@@ -4,6 +4,7 @@
     "com.unity.ide.vscode": "1.2.3",
     "com.unity.multiplayer-hlapi": "1.0.8",
     "com.unity.test-framework": "1.1.24",
+    "com.google.ar.core.arfoundation.extensions": "https://github.com/google-ar/arcore-unity-extensions.git",
     "com.unity.ugui": "1.0.0",
     "com.unity.xr.arcore": "4.2.0-pre.7",
     "com.unity.xr.arfoundation": "4.2.0-pre.7",