Implement IShader and ISwapChain interfaces for D3D12 backend

- D3D12Shader now implements IShader interface with GetBytecode, GetBytecodeSize, GetType, GetInputLayout
- D3D12SwapChain now implements ISwapChain interface with GetBackBuffer returning IResource*
- Added D3D12Texture back buffer storage to SwapChain
- Fixed ISwapChain const correctness (GetCurrentBackBufferIndex, GetBackBuffer)
- main.cpp: use GetD3D12Bytecode() instead of GetBytecode() for PSO creation

engine/src/RHI/D3D12/D3D12Shader.cpp

@@ -57,7 +57,7 @@ void D3D12Shader::Shutdown() {
     m_error.Reset();
 }
 
-const D3D12_SHADER_BYTECODE D3D12Shader::GetBytecode() const {
+const D3D12_SHADER_BYTECODE D3D12Shader::GetD3D12Bytecode() const {
     D3D12_SHADER_BYTECODE bytecode = {};
     if (m_bytecode) {
         bytecode.pShaderBytecode = m_bytecode->GetBufferPointer();
@@ -66,5 +66,27 @@ const D3D12_SHADER_BYTECODE D3D12Shader::GetBytecode() const {
     return bytecode;
 }
 
+const void* D3D12Shader::GetBytecode() const {
+    if (m_bytecode) {
+        return m_bytecode->GetBufferPointer();
+    }
+    return nullptr;
+}
+
+size_t D3D12Shader::GetBytecodeSize() const {
+    if (m_bytecode) {
+        return m_bytecode->GetBufferSize();
+    }
+    return 0;
+}
+
+const InputLayoutDesc& D3D12Shader::GetInputLayout() const {
+    return m_inputLayout;
+}
+
+ShaderType D3D12Shader::GetType() const {
+    return m_type;
+}
+
 } // namespace RHI
 } // namespace XCEngine