[SR-223] Option to assume ObjC return values are always nullable

[swift-ci]

Previous ID	SR-223
Radar	None
Original Reporter	ultramiraculous (JIRA User)
Type	Improvement

Additional Detail from JIRA

Votes	1
Component/s
Labels	Improvement
Assignee	None
Priority	Medium

md5: 807459f0cb45811e0f8f067d612e0a07

relates to:

• SR-104 Improve Crash-Safety when Importing Objective-C Code Without Nullability Attributes

Issue Description:

Would it be possible to get either an option to change the compiler behavior to choose different nullability behavior or give a companion to `NS_ASSUME_NONNULL_BEGIN` with the opposite effect?

As is, applying `null_unspecified` to everything coming out of ObjC seems to encourage unsafe assumptions about what you're getting out of an ObjC function.