chore: refactor context isolation spec (#14394)

* spec: refactor BrowserWindow module contextIsolation option

* spec: check for serialzation in isolated renderers separately

spec/fixtures/api/isolated-preload.js

@@ -1,7 +1,3 @@
-// Ensure fetch works from isolated world origin
-fetch('http://localhost:1234')
-fetch('https://localhost:1234')
-
 const {ipcRenderer, webFrame} = require('electron')
 
 window.foo = 3
@@ -16,18 +12,8 @@ window.addEventListener('message', (event) => {
       typeofRequire: typeof require,
       typeofProcess: typeof process,
       typeofArrayPush: typeof Array.prototype.push,
-      typeofFunctionApply: typeof Function.prototype.apply
-    },
-    pageContext: event.data
-  })
-  ipcRenderer.send('isolated-sandbox-world', {
-    preloadContext: {
-      preloadProperty: typeof window.foo,
-      pageProperty: typeof window.hello,
-      typeofRequire: typeof require,
-      typeofProcess: typeof process,
-      typeofArrayPush: typeof Array.prototype.push,
-      typeofFunctionApply: typeof Function.prototype.apply
+      typeofFunctionApply: typeof Function.prototype.apply,
+      typeofPreloadExecuteJavaScriptProperty: typeof window.preloadExecuteJavaScriptProperty
     },
     pageContext: event.data
   })