Goals
* Reflect Apple nullability annotations in our bindings using C#8
* No warnings when building bindings
Non-Goals
* Update (add or fix) `[NullAllowed]` to match Apple headers (next phase)
* Make the generator or internal code fully nullable aware (`nowarn` is used)
Notes
* Apple's own annotations are not 100% accurate :(
* Where known issue exists we have _fixed_ our attributes to match reality :)
* We also do additional null-checks internally that might seems not required (better safe than sorry).
Only one to start... it's been discussed before but we generally
found other ways to do them. Let's continue to pick the best place
but we now have more options :)
Sebastien Pouliot