Kotlin: Give fields a Kotlin type

This meant refactoring the EnumEntry extraction a bit. The IR doesn't
give us a type for fields, so we have to make it up based on the parent.

java/ql/lib/config/semmlecode.dbscheme

@@ -353,6 +353,7 @@ fields(
   unique int id: @field,
   string nodeName: string ref,
   int typeid: @type ref,
+  int kttypeid: @kt_type ref,
   int parentid: @reftype ref,
   int sourceid: @field ref
 );