feat: 实现 D3D12RootSignature 根签名类

- 添加 D3D12RootSignature.h 头文件
- 实现 ID3D12RootSignature 封装
- 支持序列化根签名描述符
- 测试通过

engine/src/RHI/D3D12RootSignature.cpp

@@ -0,0 +1,41 @@
+#include "XCEngine/RHI/D3D12/D3D12RootSignature.h"
+
+namespace XCEngine {
+namespace RHI {
+
+D3D12RootSignature::D3D12RootSignature() {
+}
+
+D3D12RootSignature::~D3D12RootSignature() {
+    Shutdown();
+}
+
+bool D3D12RootSignature::Initialize(ID3D12Device* device, const D3D12_ROOT_SIGNATURE_DESC& desc) {
+    ID3DBlob* signature = nullptr;
+    ID3DBlob* error = nullptr;
+
+    HRESULT hResult = D3D12SerializeRootSignature(&desc, D3D_ROOT_SIGNATURE_VERSION_1, &signature, &error);
+    if (FAILED(hResult)) {
+        if (error) {
+            error->Release();
+        }
+        return false;
+    }
+
+    hResult = device->CreateRootSignature(0, signature->GetBufferPointer(), signature->GetBufferSize(), IID_PPV_ARGS(&m_rootSignature));
+    
+    signature->Release();
+    
+    if (FAILED(hResult)) {
+        return false;
+    }
+
+    return true;
+}
+
+void D3D12RootSignature::Shutdown() {
+    m_rootSignature.Reset();
+}
+
+} // namespace RHI
+} // namespace XCEngine