lib: make navigator properties lazy

Noticed in some benchmarking/profiling that the Navigator object
constructor was rather expensive and slow due to initialization
of properties during construction. It makes more sense for these
to be lazily initialized on first access.

Author: jasnell

lib/internal/navigator.js

@@ -78,10 +78,10 @@ function getNavigatorPlatform(process) {
 class Navigator {
   // Private properties are used to avoid brand validations.
   #availableParallelism;
-  #userAgent = `Node.js/${StringPrototypeSlice(nodeVersion, 1, StringPrototypeIndexOf(nodeVersion, '.'))}`;
-  #platform = getNavigatorPlatform(process);
-  #language = Intl?.Collator().resolvedOptions().locale || 'en-US';
-  #languages = ObjectFreeze([this.#language]);
+  #userAgent;
+  #platform;
+  #language;
+  #languages;
 
   constructor() {
     if (arguments[0] === kInitialize) {
@@ -102,27 +102,31 @@ class Navigator {
    * @return {string}
    */
   get language() {
+    this.#language ??= Intl?.Collator().resolvedOptions().locale || 'en-US';
     return this.#language;
   }
 
   /**
    * @return {Array<string>}
    */
   get languages() {
+    this.#languages ??= ObjectFreeze([this.#language]);
     return this.#languages;
   }
 
   /**
    * @return {string}
    */
   get userAgent() {
+    this.#userAgent ??=`Node.js/${StringPrototypeSlice(nodeVersion, 1, StringPrototypeIndexOf(nodeVersion, '.'))}`;
     return this.#userAgent;
   }
 
   /**
    * @return {string}
    */
   get platform() {
+    this.#platform ??= getNavigatorPlatform(process);
     return this.#platform;
   }
 }