[0.76] Cleanup ReactNativeAppBuilder and ReactNativeWin32App (#14025)

This PR backports #13983 to 0.76.

## Description

This PR simplifies and scopes down the API for `ReactNativeAppBuilder` and `ReactNativeWin32App`.

### Type of Change
- Bug fix (non-breaking change which fixes an issue)

### Why
`ReactNativeAppBuilder`'s API surface made it too easy to call incorrectly and not realize it.

Resolves #13946

### What

There are a variety of changes to the API surface:
* `ReactInstanceSettingsBuilder` deleted: not only are there are simply too many APIs that would need to be exposed to be useful, the very act of creating and replacing the app's `ReactNativeHost`'s `ReactInstanceSettings` with a new one is what caused the bug in #13946 in the first place
* `ReactNativeAppBuilder` now only exposes APIs to specify the intial, non-ReactNative, WinAppSDK types, (i.e. `DispatcherQueueController`, `Compositor`, and `AppWindow`), objects the app developer may already have created for their existing app, and otherwise is only responsible for building a `ReactNativeWin32App` with those types properly pre-made
* `ReactNativeWin32App::Start()` is now more responsible for the stitching together all of the relevant types to make a working Win32 fabric app
* All WinRT APIs without an immediate use-case have been commented out until we are sure they are necessary and that it is safe to expose them
* The template has been updated to follow the pattern of:
    * Use `ReactNativeAppBuilder` to get a `ReactNativeWin32` app with the base WinAppSDK types ready
    * Get and modify the types as necessary from the created app object (like the `ReactInstanceSettings` and the `AppWindow`)
    * Call `app.Start()`

## Screenshots
N/A

## Testing
Verified new apps and example apps in libraryes build and run properly.

## Changelog
Should this change be included in the release notes: _yes_

Cleanup ReactNativeAppBuilder and ReactNativeWin32App

change/react-native-windows-2b4a6ca8-3a50-4be5-8b1d-559946fa0be1.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "[0.76] Cleanup ReactNativeAppBuilder and ReactNativeWin32App",
+  "packageName": "react-native-windows",
+  "email": "[email protected]",
+  "dependentChangeType": "patch"
+}

packages/sample-app-fabric/windows/SampleAppFabric/SampleAppFabric.cpp

@@ -8,6 +8,7 @@
 
 #include "NativeModules.h"
 
+// A PackageProvider containing any turbo modules you define within this app project
 struct CompReactPackageProvider
     : winrt::implements<CompReactPackageProvider, winrt::Microsoft::ReactNative::IReactPackageProvider> {
  public: // IReactPackageProvider
@@ -16,65 +17,66 @@ struct CompReactPackageProvider
   }
 };
 
-// Global Variables:
-constexpr PCWSTR windowTitle = L"sample_app_fabric";
-constexpr PCWSTR mainComponentName = L"sample_app_fabric";
-
+// The entry point of the Win32 application
 _Use_decl_annotations_ int CALLBACK WinMain(HINSTANCE instance, HINSTANCE, PSTR /* commandLine */, int showCmd) {
-  // Initialize WinRT.
+  // Initialize WinRT
   winrt::init_apartment(winrt::apartment_type::single_threaded);
 
   // Enable per monitor DPI scaling
   SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2);
 
-  // Create a top-level window.
-  auto window = winrt::Microsoft::UI::Windowing::AppWindow::Create();
-  window.Title(windowTitle);
-  window.Resize({1000, 1000});
-  window.Show();
-
+  // Find the path hosting the app exe file
   WCHAR appDirectory[MAX_PATH];
   GetModuleFileNameW(NULL, appDirectory, MAX_PATH);
   PathCchRemoveFileSpec(appDirectory, MAX_PATH);
 
-  // DebugBundlePath is used when loading from a bundle server such as metro. If this parameter
-  // is not provided fallback to a combination of JavaScriptBundleFile and BundleRootPath
-  auto reactInstanceSettingsBuilder {
-    winrt::Microsoft::ReactNative::ReactInstanceSettingsBuilder()
-        .DebugBundlePath(L"index")
-        .JavaScriptBundleFile(L"index.windows")
-        .BundleRootPath(appDirectory)
+  // Create a ReactNativeWin32App with the ReactNativeAppBuilder
+  auto reactNativeWin32App{winrt::Microsoft::ReactNative::ReactNativeAppBuilder().Build()};
+
+  // Configure the initial InstanceSettings for the app's ReactNativeHost
+  auto settings{reactNativeWin32App.ReactNativeHost().InstanceSettings()};
+  // Register any autolinked native modules
+  RegisterAutolinkedNativeModulePackages(settings.PackageProviders());
+  // Register any native modules defined within this app project
+  settings.PackageProviders().Append(winrt::make<CompReactPackageProvider>());
+
 #if BUNDLE
-        .UseFastRefresh(false)
+  // Load the JS bundle from a file (not Metro):
+  // Set the path (on disk) where the .bundle file is located
+  settings.BundleRootPath(std::wstring(L"file://").append(appDirectory).append(L"\\Bundle\\").c_str());
+  // Set the name of the bundle file (without the .bundle extension)
+  settings.JavaScriptBundleFile(L"index.windows");
+  // Disable hot reload
+  settings.UseFastRefresh(false);
 #else
-        .UseFastRefresh(true)
+  // Load the JS bundle from Metro
+  settings.JavaScriptBundleFile(L"index");
+  // Enable hot reload
+  settings.UseFastRefresh(true);
 #endif
 #if _DEBUG
-        .UseDirectDebugger(true)
-        .UseDeveloperSupport(true)
+  // For Debug builds
+  // Enable Direct Debugging of JS
+  settings.UseDirectDebugger(true);
+  // Enable the Developer Menu
+  settings.UseDeveloperSupport(true);
 #else
-        .UseDirectDebugger(false)
-        .UseDeveloperSupport(false)
+  // For Release builds:
+  // Disable Direct Debugging of JS
+  settings.UseDirectDebugger(false);
+  // Disable the Developer Menu
+  settings.UseDeveloperSupport(false);
 #endif
-  };
-
-  auto packageProviders{winrt::single_threaded_vector<winrt::Microsoft::ReactNative::IReactPackageProvider>()};
-
-  RegisterAutolinkedNativeModulePackages(packageProviders);
-  packageProviders.Append(winrt::make<CompReactPackageProvider>());
-
-  winrt::Microsoft::ReactNative::ReactViewOptions viewOptions;
-  viewOptions.ComponentName(mainComponentName);
 
-  // Initialize and Manage the ReactNativeHost
-  auto reactNativeAppBuilder{winrt::Microsoft::ReactNative::ReactNativeAppBuilder()
-                                 .AddPackageProviders(packageProviders)
-                                 .SetReactInstanceSettings(reactInstanceSettingsBuilder.ReactInstanceSettings())
-                                 .SetAppWindow(window)
-                                 .SetReactViewOptions(viewOptions)};
+  // Get the AppWindow so we can configure its initial title and size
+  auto appWindow{reactNativeWin32App.AppWindow()};
+  appWindow.Title(L"sample_app_fabric");
+  appWindow.Resize({1000, 1000});
 
-  // Start the react-native instance by creating a javascript runtime and load the bundle.
-  auto reactNativeWin32App{reactNativeAppBuilder.Build()};
+  // Get the ReactViewOptions so we can set the initial RN component to load
+  auto viewOptions{reactNativeWin32App.ReactViewOptions()};
+  viewOptions.ComponentName(L"sample_app_fabric");
 
+  // Start the app
   reactNativeWin32App.Start();
 }