Figure out if
* we're missing enum values (easy to workaround, but annoying for developers)
* we expose enum values that are not defined natively (potential bugs)
reference: https://github.com/xamarin/xamarin-macios/issues/7527
Enabling this will ensure that future bindings (and Xcode updates that
change nullability information) are spotted right away.
The binding fixes are **not** complete, i.e. what was done was mostly
to debug the xtro rule and find corner cases. The backlog will be
_ignored_ so the builds won't fail.
* Not every old annotations have been migrated (work in progress, to be completed in another PR);
* Sanitation of the data files (e.g. removal of dupes and fixed, by Apple, entries) is done, but not automated (also a work in progress)
Even then this is immediately useful, i.e. better merged before 15.6 gets branched.