store recursive types in ungrammar

[lrlna]

There are three instances in our ungrammar file that are meant to be recursive but are currently not: DirectiveLocations, UnionMemberTypes and ImplementsInterfaces. We should figure out the best way to use ungrammar to record this information.

Current DirectiveLocations ungrammar:

DirectiveLocations =
  DirectiveLocation*

Should encompass this in the future:

 DirectiveLocations
   '|'? DirectiveLocation
    | DirectiveLocations '|' DirectiveLocation

Current UnionMemberTypes ungrammar:

UnionMemberTypes =
  '=' '|'? NamedType*

Should encompass this:

 UnionMemberTypes =
   '=' '|'? NamedType
    | UnionMemberTypes '|' NamedType
// maybe using this:
UnionMemberTypes =
   `'=' '|'? (NamedType '|')* NamedType`