Remove await for WASM platform.callEntryPoint (#31997)

* Remove await for WASM `platform.callEntryPoint`

Also added an E2E test.

Addresses #31971

Insertion into preview 4: #31978

* Update src/Components/test/E2ETest/Tests/StandaloneAppTest.cs

Author: TanayParikh

src/Components/Web.JS/src/Boot.WebAssembly.ts

@@ -119,7 +119,7 @@ async function boot(options?: Partial<WebAssemblyStartOptions>): Promise<void> {
   }
 
   // Start up the application
-  await platform.callEntryPoint(resourceLoader.bootConfig.entryAssembly);
+  platform.callEntryPoint(resourceLoader.bootConfig.entryAssembly);
 }
 
 function invokeJSFromDotNet(callInfo: Pointer, arg0: any, arg1: any, arg2: any): any {

src/Components/WebAssembly/testassets/StandaloneApp/wwwroot/index.html

@@ -18,6 +18,13 @@
         <a class="dismiss">🗙</a>
     </div>
 
-    <script src="_framework/blazor.webassembly.js"></script>
+    <script src="_framework/blazor.webassembly.js" autostart="false"></script>
+    <script>
+        (function(){
+            Blazor.start().then(function () {
+                window['__aspnetcore__testing__blazor_wasm__started__'] = true;
+            });
+        })();
+    </script>
 </body>
 </html>

src/Components/test/E2ETest/Tests/StandaloneAppTest.cs

@@ -108,6 +108,22 @@ public void HasFetchDataPage()
             }
         }
 
+        [Fact]
+        public void IsStarted()
+        {
+            // Read from property
+            var jsExecutor = (IJavaScriptExecutor)Browser;
+
+            var isStarted = jsExecutor.ExecuteScript("return window['__aspnetcore__testing__blazor_wasm__started__'];");
+            if (isStarted is null)
+            {
+                throw new InvalidOperationException("Blazor wasm started value not set");
+            }
+
+            // Confirm server has started
+            Assert.True((bool)isStarted);
+        }
+
         private void WaitUntilLoaded()
         {
             var app = Browser.Exists(By.TagName("app"));