RHI: Add DescriptorSet abstraction for D3D12 and OpenGL backends

- Add RHIDescriptorSet base class with Update/UpdateSampler/GetNativeHandle
- Add RHIDescriptorPool with AllocateSet/FreeSet methods
- Add SetGraphicsDescriptorSets/SetComputeDescriptorSets to RHICommandList
- Implement D3D12DescriptorSet using descriptor heap allocation
- Implement OpenGLDescriptorSet using TextureUnitAllocator
- Add CreateDescriptorPool/CreateDescriptorSet factory methods to RHIDevice
- Fix unit test SetVertexBuffer -> SetVertexBuffers API
- Add SetVertexBuffer convenience method for D3D12 backward compatibility
- Update CMakeLists.txt with new source files

engine/src/RHI/OpenGL/OpenGLCommandList.cpp

@@ -4,6 +4,7 @@
 #include "XCEngine/RHI/OpenGL/OpenGLShader.h"
 #include "XCEngine/RHI/OpenGL/OpenGLFramebuffer.h"
 #include "XCEngine/RHI/OpenGL/OpenGLRenderPass.h"
+#include "XCEngine/RHI/OpenGL/OpenGLDescriptorSet.h"
 #include <glad/glad.h>
 
 namespace XCEngine {
@@ -650,6 +651,38 @@ void OpenGLCommandList::SetPipelineState(RHIPipelineState* pipelineState) {
     }
 }
 
+void OpenGLCommandList::SetGraphicsDescriptorSets(
+    uint32_t firstSet,
+    uint32_t count,
+    RHIDescriptorSet** descriptorSets,
+    RHIPipelineLayout* pipelineLayout) {
+    (void)firstSet;
+    (void)pipelineLayout;
+    
+    for (uint32_t i = 0; i < count; ++i) {
+        if (descriptorSets[i] != nullptr) {
+            OpenGLDescriptorSet* glSet = static_cast<OpenGLDescriptorSet*>(descriptorSets[i]);
+            glSet->Bind();
+        }
+    }
+}
+
+void OpenGLCommandList::SetComputeDescriptorSets(
+    uint32_t firstSet,
+    uint32_t count,
+    RHIDescriptorSet** descriptorSets,
+    RHIPipelineLayout* pipelineLayout) {
+    (void)firstSet;
+    (void)pipelineLayout;
+    
+    for (uint32_t i = 0; i < count; ++i) {
+        if (descriptorSets[i] != nullptr) {
+            OpenGLDescriptorSet* glSet = static_cast<OpenGLDescriptorSet*>(descriptorSets[i]);
+            glSet->Bind();
+        }
+    }
+}
+
 void OpenGLCommandList::SetVertexBuffers(uint32_t startSlot, uint32_t count, RHIResourceView** buffers, const uint64_t* offsets, const uint32_t* strides) {
     for (uint32_t i = 0; i < count; i++) {
         if (!buffers[i]) continue;