Add basic non-complete GL hooking on apple

* We implement this with dyld interposing. This means we must decide at compile
  time which functions to be hooked - in particular we require a manually
  curated list of functions that are actually exposed in the latest macOS GL
  version. Fortunately this is not a moving target anymore so this list should
  now be complete.
* The hooking is not complete:
  - It doesn't do full context tracking, just context create and make current
  - There's no drawable/window querying or tracking, so windows aren't properly processed and their size is wrong
* Also note that this does not support the replay side yet (CGLPlatform is still
  mostly stubs) and capturing actually still crashes.