Usage of Span was temporarily behind an experimental feature flag. Now
that SE-0447 has been accepted, remove the experimental feature flag and
allow Span usage everywhere.
Implements rdar://144819992.
When we generate a safe wrapper that only differs in the return type we
might introduce ambiguities as some callers might not have enough
information to disambiguate between the overloads. This PR makes sure
the newly generated declarations are marked as @_disfavoredOverload so
the compiler can keep calling the old functions without a source break
when the feature is turned on.
rdar://139074571
This passes along the noescape attribute to @_SwiftifyImport as
.noescape(pointer: .param(X)). This allows importing parameters as Span,
MutableSpan and RawSpan.
