RHI: Internalize OpenGL-specific methods in OpenGLDevice

- Remove GetTextureUnitAllocator/GetUniformBufferManager from public interface
- Remove SwapBuffers from public interface (friend OpenGLSwapChain can still access)
- Add MakeContextCurrent() and GetNativeContext() public methods
- Update integration tests to use MakeContextCurrent() instead of wglMakeCurrent
- Update RenderDoc calls to use GetNativeContext() instead of GetGLContext()
- Remove Device_SwapBuffers_NoErrors test (SwapBuffers no longer public)
- Mark Priority 7 as completed in RHI_Design_Issues.md

engine/include/XCEngine/RHI/OpenGL/OpenGLDevice.h

@@ -29,14 +29,10 @@ public:
     void Shutdown() override;
 
     bool InitializeWithExistingWindow(HWND hwnd);
-    HDC GetPresentationDC() const { return m_hdc; }
-    HGLRC GetGLContext() const { return m_hglrc; }
     const RHIDeviceInfo& GetDeviceInfoImpl() const { return m_deviceInfo; }
 
-    OpenGLTextureUnitAllocator* GetTextureUnitAllocator() { return m_textureUnitAllocator.get(); }
-    OpenGLUniformBufferManager* GetUniformBufferManager() { return m_uniformBufferManager.get(); }
-
-    void SwapBuffers();
+    bool MakeContextCurrent();
+    void* GetNativeContext() const { return m_hglrc; }
 
     RHIBuffer* CreateBuffer(const BufferDesc& desc) override;
     RHITexture* CreateTexture(const TextureDesc& desc) override;
@@ -66,6 +62,11 @@ public:
 private:
     friend class OpenGLSwapChain;
 
+    HDC GetPresentationDC() const { return m_hdc; }
+    OpenGLTextureUnitAllocator* GetTextureUnitAllocator() { return m_textureUnitAllocator.get(); }
+    OpenGLUniformBufferManager* GetUniformBufferManager() { return m_uniformBufferManager.get(); }
+    void SwapBuffers();
+
     HWND m_hwnd = nullptr;
     HDC m_hdc = nullptr;
     HGLRC m_hglrc = nullptr;