Use centralized OpenGLEnums.h for enum conversion:
- Remove local ToGL* functions from OpenGLCommandList
- Replace with ToOpenGL() and ToOpenGLClearBuffer() from OpenGLEnums
- Simplify OpenGLTexture, OpenGLBuffer, OpenGLSampler, etc.
- Simplify OpenGL integration test structure
- Enable CTest registration for OpenGL tests
- Refactor test fixtures and device enumeration
- Minor code cleanup and improvements
- 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