base::iter_structural_ty: tuples
base::iter_structural_ty: structs and records
Convert iter_structural_ty to trans::adt
whitespace
Convert trans_tuple_struct to trans::adt.

Surely this cannot be the best way to get the type.
glue::trans_struct_drop -> adt
Finish removing struct layout dependencies from glue.
GC the now-unused old layout helpers
Bonus Fix: typarams are no longer inhabited