This highly improves interop with Swift. It would map all
pointers as implicitly unwrapped optionals, which skip all
null safety checks. Adding `_Nullable` to pointer types
makes swift map them as optionals.
Also constructors are now nullable since it's valid to return nil from
Go code.
Change-Id: If0506bb80f31bf36f11522c16a1e66d77be935f8
GitHub-Last-Rev: bd6c30f7f50ef5ea5797b07073f0a4a70d545025
GitHub-Pull-Request: golang/mobile#26
Reviewed-on: https://go-review.googlesource.com/c/mobile/+/159477
Run-TryBot: Elias Naur <mail@eliasnaur.com>
Reviewed-by: Elias Naur <mail@eliasnaur.com>