Move OpenGL backend classes from tests/OpenGL to engine/

- Relocated OpenGLDevice, OpenGLShader, OpenGLBuffer, OpenGLVertexArray, OpenGLTexture to engine/
- Updated engine/CMakeLists.txt to include OpenGL backend source files
- Updated tests/OpenGL/CMakeLists.txt to use engine backend
- Added OpenGLTexture class implementation

engine/src/RHI/OpenGL/OpenGLBuffer.cpp

@@ -0,0 +1,61 @@
+#define GLFW_INCLUDE_NONE
+#include "XCEngine/RHI/OpenGL/OpenGLBuffer.h"
+#include <glad/glad.h>
+#include <GLFW/glfw3.h>
+
+namespace XCEngine {
+namespace RHI {
+
+OpenGLBuffer::OpenGLBuffer()
+    : m_buffer(0)
+    , m_size(0)
+    , m_isIndexBuffer(false) {
+}
+
+OpenGLBuffer::~OpenGLBuffer() {
+    Shutdown();
+}
+
+bool OpenGLBuffer::InitializeVertexBuffer(const void* data, size_t size) {
+    glGenBuffers(1, &m_buffer);
+    glBindBuffer(GL_ARRAY_BUFFER, m_buffer);
+    glBufferData(GL_ARRAY_BUFFER, size, data, GL_STATIC_DRAW);
+    m_size = size;
+    m_isIndexBuffer = false;
+    return true;
+}
+
+bool OpenGLBuffer::InitializeIndexBuffer(const void* data, size_t size) {
+    glGenBuffers(1, &m_buffer);
+    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_buffer);
+    glBufferData(GL_ELEMENT_ARRAY_BUFFER, size, data, GL_STATIC_DRAW);
+    m_size = size;
+    m_isIndexBuffer = true;
+    return true;
+}
+
+void OpenGLBuffer::Shutdown() {
+    if (m_buffer) {
+        glDeleteBuffers(1, &m_buffer);
+        m_buffer = 0;
+    }
+}
+
+void OpenGLBuffer::Bind() const {
+    if (m_isIndexBuffer) {
+        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_buffer);
+    } else {
+        glBindBuffer(GL_ARRAY_BUFFER, m_buffer);
+    }
+}
+
+void OpenGLBuffer::Unbind() const {
+    if (m_isIndexBuffer) {
+        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
+    } else {
+        glBindBuffer(GL_ARRAY_BUFFER, 0);
+    }
+}
+
+} // namespace RHI
+} // namespace XCEngine