[Embedder API] Fix test helper's present callback registration (#51560)

#51293 added a new present callback that supports multiple views. However, the test helper incorrectly inversed the single-view and multi-view present callbacks. This didn't affect the existing tests as we don't any multi-view tests yet.

Prepares for flutter/flutter#144810

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: loic-sharma

shell/platform/embedder/tests/embedder_config_builder.cc

@@ -377,14 +377,6 @@ void EmbedderConfigBuilder::SetCompositor(bool avoid_backing_store_cache,
             ->CollectBackingStore(backing_store);
       };
   if (use_present_layers_callback) {
-    compositor_.present_view_callback = [](const FlutterPresentViewInfo* info) {
-      auto compositor =
-          reinterpret_cast<EmbedderTestCompositor*>(info->user_data);
-
-      return compositor->Present(info->view_id, info->layers,
-                                 info->layers_count);
-    };
-  } else {
     compositor_.present_layers_callback = [](const FlutterLayer** layers,
                                              size_t layers_count,
                                              void* user_data) {
@@ -394,6 +386,14 @@ void EmbedderConfigBuilder::SetCompositor(bool avoid_backing_store_cache,
       // it can only be used to render the implicit view.
       return compositor->Present(kFlutterImplicitViewId, layers, layers_count);
     };
+  } else {
+    compositor_.present_view_callback = [](const FlutterPresentViewInfo* info) {
+      auto compositor =
+          reinterpret_cast<EmbedderTestCompositor*>(info->user_data);
+
+      return compositor->Present(info->view_id, info->layers,
+                                 info->layers_count);
+    };
   }
   compositor_.avoid_backing_store_cache = avoid_backing_store_cache;
   project_args_.compositor = &compositor_;