cocoa: Implement OpenGL swap interval support with CVDisplayLink.

Not only does this fix macOS 10.14 ("Mojave")'s broken NSOpenGLCPSwapInterval
support, it also lets us implement "adaptive vsync" on macOS!

CVDisplayLink is supported back to macOS 10.4 ("Tiger"), so we just use it
universally without version checks and dump NSOpenGLCPSwapInterval, Mojave or
not.

--HG--
extra : rebase_source : 158673908a50df9b28519d5674c8444e078546c6
2 files changed