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).
This has a couple of advantages:
* It makes it easier to add a catalyst version of these libraries (because it
becomes cumbersome to build for catalyst when the build rules assumes we're
building for both simulator and device).
* It makes it easier to create an xcframework of our libraries, because the
contents in an xcframework is split like this.
Sebastien Pouliot
Rolf Bjarne Kvinge