caopengllayer: try to select low power gpu on macos

VLC is not very demanding in OpenGL usage. Try to use low power GPU even if it is not the default one selected by the OS.

On some system like MacBook Pro Intel with AMD card, creating the GL context will always activate the discrete GPU (i.e. the AMD GPU here). This is not an issue for 99% of the case when the renderer context is here to provide the maximum performance level like for game. However, for video application using GPU for 1 quad and 1 texture, using the discrete GPU for that lead to an important power consumption (4 to 8W), heat increase, and fan noise. With this patch, I successfully force VLC to use the integrated GPU (i.e. the Intel one), instead of the discrete GPU (i.e. the AMD one). This does not seems to introduce drawback on the configurations I've tested: - no external screen, the iGPU is used, video are rendered correctly - multiple screens with one screen on eGPU, the iGPU is used, video are rendered correctly and can be move across screens