swift234

Better diagnose error coming from unwrapping optional before initialized.

Added a check for whether the escape use is due to an
UncheckedTakeEnumDataAddrInst, which accesses the memory to grab the
.Some part of an Optional during “?.” or “!”. In that case, use the
generic used-before-initialized diagnostic, since it isn’t actually
because of closure capture.

Added test cases, including specifically testing that capturing in a
closure in order to unwrap the optional is still ok.