swift234

Verify that a function's DeclName, TuplePattern, and ParamDecls are in sync.

This required a few changes in places where we synthesize functions to
make sure these properties hold. That's good because we don't know where
we might already be depending on them. (On the other hand, we could also
decide not to care about TuplePattern labels, in which case I wonder if
we could eventually discard them altogether in functions.)

Still untested: that the function type is also in sync.