Add OpenGL backend: OpenGLDevice class

- Created OpenGLDevice class for window and OpenGL context management
- Added CreateWindow() and InitializeWithExistingWindow() methods
- Integrated with GLFW and GLAD
- Added to tests/OpenGL as test target

This is the first step in building the OpenGL RHI backend parallel to D3D12.

tests/OpenGL/OpenGLDevice.cpp

@@ -0,0 +1,95 @@
+#define GLFW_INCLUDE_NONE
+#include "OpenGLDevice.h"
+#include <glad/glad.h>
+#include <GLFW/glfw3.h>
+
+namespace XCEngine {
+namespace RHI {
+
+OpenGLDevice::OpenGLDevice()
+    : m_window(nullptr)
+    , m_initialized(false)
+    , m_ownsWindow(false) {
+}
+
+OpenGLDevice::~OpenGLDevice() {
+    Shutdown();
+}
+
+bool OpenGLDevice::CreateWindow(int width, int height, const char* title, bool enableDebug) {
+    if (m_initialized) {
+        return true;
+    }
+
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
+    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
+
+    m_window = glfwCreateWindow(width, height, title, nullptr, nullptr);
+    if (!m_window) {
+        return false;
+    }
+
+    m_ownsWindow = true;
+    return InitializeWithExistingWindow(m_window);
+}
+
+bool OpenGLDevice::InitializeWithExistingWindow(GLFWwindow* window) {
+    if (m_initialized) {
+        return true;
+    }
+
+    m_window = window;
+    if (!m_window) {
+        return false;
+    }
+
+    glfwMakeContextCurrent(m_window);
+
+    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) {
+        return false;
+    }
+
+    m_deviceInfo.vendor = reinterpret_cast<const char*>(glGetString(GL_VENDOR));
+    m_deviceInfo.renderer = reinterpret_cast<const char*>(glGetString(GL_RENDERER));
+    m_deviceInfo.version = reinterpret_cast<const char*>(glGetString(GL_VERSION));
+    
+    glGetIntegerv(GL_MAJOR_VERSION, &m_deviceInfo.majorVersion);
+    glGetIntegerv(GL_MINOR_VERSION, &m_deviceInfo.minorVersion);
+
+    m_initialized = true;
+    return true;
+}
+
+void OpenGLDevice::Shutdown() {
+    if (m_ownsWindow && m_window) {
+        glfwDestroyWindow(m_window);
+    }
+    m_window = nullptr;
+    m_initialized = false;
+    m_ownsWindow = false;
+}
+
+void OpenGLDevice::SwapBuffers() {
+    if (m_window) {
+        glfwSwapBuffers(m_window);
+    }
+}
+
+bool OpenGLDevice::PollEvents() {
+    glfwPollEvents();
+    return !glfwWindowShouldClose(m_window);
+}
+
+void OpenGLDevice::SetShouldClose(bool shouldClose) {
+    if (m_window) {
+        glfwSetWindowShouldClose(m_window, shouldClose ? GLFW_TRUE : GLFW_FALSE);
+    }
+}
+
+bool OpenGLDevice::ShouldClose() const {
+    return m_window && glfwWindowShouldClose(m_window) == GLFW_TRUE;
+}
+
+} // namespace RHI
+} // namespace XCEngine