Rename Impl classes to follow Unity naming convention

- SelectionManagerImpl -> SelectionManager
- EditorContextImpl -> EditorContext
- Removed unused SceneManagerImpl and ISceneManager

The Impl suffix was inconsistent with Unity naming conventions.

engine/src/RHI/D3D12/D3D12CommandAllocator.cpp

@@ -19,9 +19,8 @@ bool D3D12CommandAllocator::Initialize(ID3D12Device* device, CommandQueueType ty
         ToD3D12(type),
         IID_PPV_ARGS(&m_commandAllocator));
     if (FAILED(hResult)) {
-        char buf[256];
-        sprintf(buf, "[D3D12CommandAllocator] CreateCommandAllocator failed: hr=0x%08X\n", hResult);
-        OutputDebugStringA(buf);
+        FILE* f = fopen("D:\\Xuanchi\\Main\\XCEngine\\debug_rhi.log", "a");
+        if (f) { fprintf(f, "[D3D12CommandAllocator] CreateCommandAllocator failed: hr=0x%08X\n", hResult); fclose(f); }
     }
     return SUCCEEDED(hResult);
 }