fix: add HasFeatureFix.h to resolve __has_feature on MSVC

MSVC (VS 2022) does not define __has_feature, which is a Clang extension.
Assimp and other headers that use __has_feature(x) fail to compile under
MSVC without this guard.

- Add Source/RuntimeAssetImport/Public/HasFeatureFix.h with an
  #ifndef __has_feature / #define __has_feature(x) 0 guard.
- Include HasFeatureFix.h in AssetLoader.cpp, AssetConstructor.cpp, and
  AssetConstructorHelpers.cpp immediately after the matching header and
  before any engine or assimp headers, satisfying both UHT's include-order
  requirement and the need to define __has_feature before assimp pulls it.

The header is placed in Public/ so it can be used via forced-include
compiler flags (/FI) if needed in future, without requiring a namespace-
qualified path from Private code.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: metyatech

Source/RuntimeAssetImport/Private/AssetConstructor.cpp

@@ -2,7 +2,7 @@
 
 #include "AssetConstructor.h"
 
-#include "HasFeatureDef.h"
+#include "HasFeatureFix.h"
 #include "AssetConstructorHelpers.h"
 #include "AssetLoader.h"
 #include "CreateMeshFromMeshDataOnProceduralMeshComponentLatentAction.h"

Source/RuntimeAssetImport/Private/AssetConstructorHelpers.cpp

@@ -2,7 +2,7 @@
 
 #include "AssetConstructorHelpers.h"
 
-#include "HasFeatureDef.h"
+#include "HasFeatureFix.h"
 #include "ImageUtils.h"
 #include "LogAssetConstructor.h"
 #include "Materials/MaterialInstanceDynamic.h"

Source/RuntimeAssetImport/Private/AssetLoader.cpp

@@ -2,7 +2,7 @@
 
 #include "AssetLoader.h"
 
-#include "HasFeatureDef.h"
+#include "HasFeatureFix.h"
 #include "HAL/Platform.h"
 #include "ImageUtils.h"
 #include "LogAssetLoader.h"

Source/RuntimeAssetImport/Public/HasFeatureFix.h

@@ -0,0 +1,8 @@
+#pragma once
+
+// MSVC does not define __has_feature (it is a Clang extension).
+// Define it as a no-op macro so headers that use it (e.g. assimp) compile
+// without error under MSVC / Unreal Build Tool.
+#ifndef __has_feature
+#define __has_feature(x) 0
+#endif