Represents a punned textual data constructor field name (which is a local variable binding). The associated identifier info should be either a case patter variable or a local pattern match variable.
A data constructor field name can be associated with multiple data constructors when it appears in a case alternative containing more than one data constructor, e.g.
case foo of (DC1|DC2|DC3) {field1=bar, field2} -> ...
Both field1 and field2 are associated with DC1, DC2, and DC3, and field2 is a punned data constructor field name.
@author Joseph Wong