Convert a string representing a type (the deco) and return its equivalent Type.
Returns exact mangled name of function.
Mangle function signatures ('this' qualifier, and parameter types) to check conflicts in function overloads. It's different from fd.type.deco. For example, fd.type.deco would be null if fd is an auto function.
Does name mangling for extern(D) symbols.
Specification: Name Mangling