Enhance OpenGL RTV and DSV with comprehensive framebuffer support

OpenGLRenderTargetView:
- Add RenderTargetType enum for different texture types
- Add RenderTargetViewDesc struct with mip level, array slice, layer info
- Add Initialize() with desc parameter for 2D/2DArray/3D/Cube
- Add InitializeCubemap() for cubemap faces
- Add Bind(count) overload for multiple framebuffers
- Add Clear() methods for color and depth-stencil
- Add static BindFramebuffer/UnbindFramebuffer methods

OpenGLDepthStencilView:
- Add DepthStencilType enum for different texture types
- Add DepthStencilViewDesc struct with mip level, array slice, layer info
- Add Initialize() with desc parameter for 2D/2DArray/Cube
- Add InitializeCubemap() for cubemap faces
- Add ClearDepth, ClearStencil, ClearDepthStencil methods
- Add static BindFramebuffer/UnbindFramebuffer methods

docs/RHI抽象层设计与实现.md

@@ -60,8 +60,8 @@ engine/
 ### 4.1 目录结构调整建议
 ```
 include/XCEngine/RHI/
-├── Enums.h                  # 通用枚举
-├── Types.h                  # 通用结构体
+├── RHIEnums.h                  # 通用枚举
+├── RHITypes.h                  # 通用结构体
 ├── RHICapabilities.h        # 硬件能力检测
 ├── RHIDevice.h              # 设备抽象（核心入口）
 ├── RHICommandQueue.h        # 命令队列抽象