Initialize the ExternalServices-instance lazily in the viewer (PR 17588 follow-up)

web/app.js

@@ -145,7 +145,6 @@ const PDFViewerApplication = {
   url: "",
   baseUrl: "",
   _downloadUrl: "",
-  externalServices: new ExternalServices(),
   _boundEvents: Object.create(null),
   documentInfo: null,
   metadata: null,
@@ -676,6 +675,10 @@ const PDFViewerApplication = {
     }
   },
 
+  get externalServices() {
+    return shadow(this, "externalServices", new ExternalServices());
+  },
+
   get initialized() {
     return this._initializedCapability.settled;
   },