Whenever we visit a declaration via the DeclChecker, add it to the
list of declarations to finalize. This makes sure that we can centralize
the notion of “finalize for SILGen” and that it will be called for
everything in the source file being processed.
We don't finalize declarations when there's been an error, which means
we might never assign types to the stored properties/cases of a nominal
type from another file, which means that circularity checking for types
using those types be re-delayed.
Fixes SR-4594.
