Optimize for macOS Performance and Fix Fullscreen Letterbox Issue…

Recently, we have a performance issue on our macOS build. The game runs smoothly in low-end Windows laptops but laggy in a 2016 Macbook. Although the hardware of the Macbook is not even as good as the Windows laptop, we doubted the performance would be much different. In addition, it runs alright in Editor in Macbook but not in a build, so the hardware influence should be able to be ignored.