Remove Paper-only code from Fabric builds of Microsoft.ReactNative (#14289)

## Description

Removes most of the Paper-only code from Fabric builds of Microsoft.ReactNative. This is only a first pass - there may be more that needs to be removed (or stuff that needs to be put back in).

### Type of Change
- Bug fix (non-breaking change which fixes an issue)
- Breaking change (fix or feature that would cause existing functionality to not work as expected)

### Why
Besides nearly doubling the size of the binary files, all of the Paper-only code is functionally useless in Fabric builds, which at worse is dead weight, and at best is confusing to developers.

Resolves #13405

### What
Updated project files to not load/compile paper-only modules. Updated modules that are used by both to correctly only include the Paper or Fabric code they need.

## Screenshots

None, but here are some preliminary binary size numbers for x64 release:

| File | Paper | Fabric (Before) | Fabric (After) |
|:-|:-:|:-:|:-:|
| Microsoft.ReactNative.dll | 4.02 MB | 8.32 MB | 6.47 MB (🔻1.85 MB / 22% ) |
| Microsoft.ReactNative.winmd | 64.0 KB | 121.0 KB | 92.0KB (🔻29 KB / 24%) |

## Testing
Verified all existing tests still pass and fabric apps work.

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

Remove Paper-only code from Fabric builds of Microsoft.ReactNative

Author: jonthysell

change/react-native-windows-73433f3d-c91f-4ae8-9618-75adc965a722.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "Remove Paper-only code from Fabric builds of Microsoft.ReactNative",
+  "packageName": "react-native-windows",
+  "email": "jthysell@microsoft.com",
+  "dependentChangeType": "patch"
+}

vnext/Desktop/React.Windows.Desktop.vcxproj

@@ -149,9 +149,6 @@
       -->
       <PreprocessorDefinitions>CORE_ABI;%(PreprocessorDefinitions)</PreprocessorDefinitions>
     </Midl>
-    <Midl>
-      <PreprocessorDefinitions Condition="'$(UseFabric)' == 'true'">USE_FABRIC;%(PreprocessorDefinitions)</PreprocessorDefinitions>
-    </Midl>
   </ItemDefinitionGroup>
   <Import Project="$(ReactNativeWindowsDir)\PropertySheets\ReactCommunity.cpp.props" />
   <ItemGroup>

vnext/Microsoft.ReactNative.Cxx/ReactContext.h

@@ -65,7 +65,7 @@ struct ReactContext {
     m_handle.EmitJSEvent(eventEmitterName, eventName, MakeJSValueWriter(std::forward<TArgs>(args)...));
   }
 
-#if !defined(CORE_ABI) && !defined(__APPLE__) && !defined(CXXUNITTESTS)
+#if !defined(CORE_ABI) && !defined(USE_FABRIC) && !defined(__APPLE__) && !defined(CXXUNITTESTS)
   // Dispatch eventName event to the view.
   // args are either function arguments or a single lambda with 'IJSValueWriter const&' argument.
   template <class... TArgs>

vnext/Microsoft.ReactNative/Fabric/Composition/CompositionEventHandler.cpp

@@ -9,7 +9,6 @@
 #include <IReactContext.h>
 #include <React.h>
 #include <Views/DevMenu.h>
-#include <Views/ShadowNodeBase.h>
 #include <windows.h>
 #include <windowsx.h>
 #include <winrt/Windows.UI.Core.h>

vnext/Microsoft.ReactNative/IReactContext.cpp

@@ -4,7 +4,7 @@
 #include "pch.h"
 #include "IReactContext.h"
 #include "DynamicWriter.h"
-#ifndef CORE_ABI
+#if !defined(CORE_ABI) && !defined(USE_FABRIC)
 #include "XamlUIService.h"
 #endif
 
@@ -121,7 +121,7 @@ LoadingState ReactContext::LoadingState() noexcept {
   };
 }
 
-#ifndef CORE_ABI
+#if !defined(CORE_ABI) && !defined(USE_FABRIC)
 // Deprecated: Use XamlUIService directly.
 void ReactContext::DispatchEvent(
     xaml::FrameworkElement const &view,

vnext/Microsoft.ReactNative/IReactContext.h

@@ -46,7 +46,7 @@ struct ReactContext : winrt::implements<ReactContext, IReactContext> {
   IInspectable JSRuntime() noexcept;
   LoadingState LoadingState() noexcept;
 
-#ifndef CORE_ABI
+#if !defined(CORE_ABI) && !defined(USE_FABRIC)
   void DispatchEvent(
       xaml::FrameworkElement const &view,
       hstring const &eventName,

vnext/Microsoft.ReactNative/IReactContext.idl

@@ -5,7 +5,7 @@ import "IJSValueWriter.idl"; // The import is to be deprecated with IReactContex
 import "IReactNotificationService.idl";
 import "IReactPropertyBag.idl";
 
-#ifndef CORE_ABI
+#if !defined(CORE_ABI) && !defined(USE_FABRIC)
 #include "NamespaceRedirect.h" // The include is to be deprecated with IReactContext::DispatchEvent
 #endif
 
@@ -185,7 +185,7 @@ namespace Microsoft.ReactNative
       "It is an experimental property that may be removed or changed in a future version.")
     Object JSRuntime { get; };
 
-#ifndef CORE_ABI
+#if !defined(CORE_ABI) && !defined(USE_FABRIC)
     [deprecated("Use @XamlUIService.DispatchEvent instead", deprecate, 1)]
     DOC_STRING("Deprecated property. Use @XamlUIService.DispatchEvent instead. It will be removed in a future version.")
     void DispatchEvent(XAML_NAMESPACE.FrameworkElement view, String eventName, JSValueArgWriter eventDataArgWriter);

vnext/Microsoft.ReactNative/IReactPackageBuilder.idl

@@ -3,7 +3,7 @@
 
 import "IReactContext.idl";
 import "IReactModuleBuilder.idl";
-#ifndef CORE_ABI
+#if !defined(CORE_ABI) && !defined(USE_FABRIC)
 import "IViewManager.idl";
 #endif
 
@@ -14,7 +14,7 @@ namespace Microsoft.ReactNative
   DOC_STRING("Provides information about a custom native module. See @IReactModuleBuilder.")
   delegate Object ReactModuleProvider(IReactModuleBuilder moduleBuilder);
 
-#ifndef CORE_ABI
+#if !defined(CORE_ABI) && !defined(USE_FABRIC)
   DOC_STRING("Provides information about a custom view manager. See @IViewManager.")
   delegate IViewManager ReactViewManagerProvider();
 #endif
@@ -32,7 +32,7 @@ namespace Microsoft.ReactNative
     "NOTE: TurboModules using JSI directly will not run correctly while using @ReactInstanceSettings.UseWebDebugger")
     void AddTurboModule(String moduleName, ReactModuleProvider moduleProvider);
 
-#ifndef CORE_ABI
+#if !defined(CORE_ABI) && !defined(USE_FABRIC)
     DOC_STRING("Adds a custom view manager. See @ReactViewManagerProvider.")
     void AddViewManager(String viewManagerName, ReactViewManagerProvider viewManagerProvider);
 #endif