refactor(RHI): 将窗口管理接口从 RHIDevice 移至 RHISwapChain

- 从 RHIDevice 抽象基类中移除 PollEvents/SwapBuffers/ShouldClose/SetShouldClose 接口
- 这些功能现在应该通过 RHISwapChain 访问
- 符合设计文档中定义的分层架构

engine/src/RHI/D3D12/D3D12Device.cpp

@@ -293,20 +293,6 @@ RHIPipelineState* D3D12Device::CreatePipelineState(const PipelineStateDesc& desc
     return nullptr;
 }
 
-bool D3D12Device::PollEvents() {
-    return false;
-}
-
-void D3D12Device::SwapBuffers() {
-}
-
-bool D3D12Device::ShouldClose() const {
-    return false;
-}
-
-void D3D12Device::SetShouldClose(bool shouldClose) {
-}
-
 D3D12CommandQueue* D3D12Device::CreateCommandQueueImpl(const CommandQueueDesc& desc) {
     return nullptr;
 }