feat: implement descriptor heap with thread-safe allocation

D3D12 Resources:
- Add descriptor_handle struct with CPU/GPU handles
- Add descriptor_heap class for descriptor management
- Implement allocate() and free() methods
- Add mutex for thread-safe access
- Support all D3D12 descriptor heap types

D3D12 Core:
- Add device() function to expose main device
- Add release() template function for COM objects

Documentation:
- Add changelog for descriptor heap implementation
- Update D3D12 Wiki with descriptor heap section
- Mark descriptor heap task as completed

Engine/Engine.vcxproj

@@ -36,6 +36,7 @@
     <ClInclude Include="Graphics\Direct3D12\D3D12CommonHeader.h" />
     <ClInclude Include="Graphics\Direct3D12\D3D12Core.h" />
     <ClInclude Include="Graphics\Direct3D12\D3D12Interface.h" />
+    <ClInclude Include="Graphics\Direct3D12\D3D12Resources.h" />
     <ClInclude Include="Graphics\GraphicsPlatformInterface.h" />
     <ClInclude Include="Graphics\Renderer.h" />
     <ClInclude Include="Platform\IncludeWindowCpp.h" />
@@ -59,10 +60,14 @@
     <ClCompile Include="Core\MainWin32.cpp" />
     <ClCompile Include="Graphics\Direct3D12\D3D12Core.cpp" />
     <ClCompile Include="Graphics\Direct3D12\D3D12Interface.cpp" />
+    <ClCompile Include="Graphics\Direct3D12\D3D12Resource.cpp" />
     <ClCompile Include="Graphics\Renderer.cpp" />
     <ClCompile Include="Platform\PlatformWin32.cpp" />
     <ClCompile Include="Platform\Window.cpp" />
   </ItemGroup>
+  <ItemGroup>
+    <None Include="Graphics\Direct3D12\D3D12Resources" />
+  </ItemGroup>
   <PropertyGroup Label="Globals">
     <VCProjectVersion>17.0</VCProjectVersion>
     <Keyword>Win32Proj</Keyword>