swift234

stdlib: Add @_versioned to type referenced from @_transparent function

In fragile stdlib builds, _Cocoa(Set|Dictionary)Iterator is fixed
layout and we never need to use its metadata. In resilient builds,
it is resilient so the metadata is required for value witness
calls.

Unfortunately SIL doesn't have asserts for references to insufficiently
visible *types* yet, so this wasn't caught except by building benchmarks.