Fix ember v6 deprecate-import-view-utils-from-ember deprecation

Author: felixbuenemann

packages/ember-cli-fastboot/vendor/experimental-render-mode-rehydrate.js

@@ -4,6 +4,7 @@
     var current = document.getElementById('fastboot-body-start');
 
     var _Ember = require.has('ember') ? require('ember').default : window.Ember;
+    var _ViewUtils = require.has('@ember/-internals/views') ? require('@ember/-internals/views') : _Ember.ViewUtils;
 
     if (current && !_Ember) {
       console.error(`Experimental render mode rehydrate isn't working because it couldn't find Ember via AMD or global.
@@ -13,8 +14,8 @@ See https://github.com/ember-fastboot/ember-cli-fastboot/issues/938 for the curr
 
     if (
       current &&
-      typeof _Ember.ViewUtils.isSerializationFirstNode === 'function' &&
-      _Ember.ViewUtils.isSerializationFirstNode(current.nextSibling)
+      typeof _ViewUtils.isSerializationFirstNode === 'function' &&
+      _ViewUtils.isSerializationFirstNode(current.nextSibling)
     ) {
       _Ember.ApplicationInstance.reopen({
         _bootSync: function(options) {