This abbreviation for "if and only if" is confusing to those not coming
from a background in formal mathematics, and is frequently reported as a
type by developers reading the documentation.
This commit also changes doc comments in internal and private members,
which don't become part of the public documentation, because omitting
"iff" everywhere makes it much easier to check for any later changes
that reintroduce it.
The initializer was originally introduced without proper availability; in https://github.com/apple/swift/pull/23643, we fixed this by applying the `@_alwaysEmitIntoClient` attribute. However, this had the unfortunate side-effect that the symbol disappeared from `libswiftCore.dylib`, which somehow confuses some simulator builds.
Try to figure out what’s happening by replacing the third closure argument with an integer return value. This changes the mangled name of the bulk initializer, which should make it more obvious how/why these builds fail.
rdar://problem/49479386
Add __consuming and __owned to Set and Dictionary members where applicable.
Ignore compiler intrinsics for casting for now — their ARC behavior is covered by unit tests that need to be updated.
