[feature request] [macOS] provide a metal backend

OF is depending on GLFW to provide the path through the macOS openGL long-deprecated APIs. since macOS13 a sync bug is present and seems difficult to address https://github.com/RustyMoyher/glfw_MacVsyncFix. in order to disengage OF of GLFW (on macOS) and gain more control on the low level flow of things (esp timing), a more supported, lower backend should be investigated.

it would also remove a time-bomb as any macOS release might completely remove openGL support (or sandbox it deeper in a compositor that compromises performance further), and relying on GLFW to provide the required answers in a timely manner might not be acceptable, especially considering it is near impossible to downgrade new Apple hardware to older macOS versions.

WebGPU was evoked in https://github.com/openframeworks/openFrameworks/issues/7752#issuecomment-1816765347.