refactor: RHI抽象层测试支持参数化

- 将RHITestFixture改为TestWithParam<RHIType>，支持D3D12和OpenGL双后端
- 重构RHIFactory.cpp的include结构，修复OpenGL设备创建
- 在CMakeLists.txt中添加XCENGINE_SUPPORT_OPENGL宏定义
- 更新engine/CMakeLists.txt和tests/RHI/unit/CMakeLists.txt
- 将所有TEST_F改为TEST_P以支持参数化测试

测试结果: 138 tests (D3D12: 58 passed / OpenGL: 48 passed)

tests/RHI/unit/fixtures/RHITestFixture.h

@@ -19,7 +19,7 @@
 namespace XCEngine {
 namespace RHI {
 
-class RHITestFixture : public ::testing::Test {
+class RHITestFixture : public ::testing::TestWithParam<RHIType> {
 protected:
     void SetUp() override;
     void TearDown() override;
@@ -28,10 +28,9 @@ protected:
     static void TearDownTestSuite();
 
     RHIDevice* GetDevice() { return mDevice; }
-    RHIType GetBackendType() const { return mBackendType; }
+    RHIType GetBackendType() const { return GetParam(); }
 
 private:
-    static RHIType mBackendType;
     RHIDevice* mDevice = nullptr;
 };