Function signatures were previously redundantly stored on Function objects as well as on FunctionType objects. These two signature representations had to always be kept in sync, which was error-prone and needlessly complex. This PR takes advantage of the new ability of Type to represent multiple value types by consolidating function signatures as a pair of Types (params and results) stored on the Function object. Since there are no longer module-global named function types, significant changes had to be made to the printing and emitting of function types, as well as their parsing and manipulation in various passes. The C and JS APIs and their tests also had to be updated to remove named function types.