tyThingLocalGREs: include all DataCons for RecFlds

The GREInfo for a record field should include the collection of all
the data constructors of the parent TyCon that have this record field.
This information was being incorrectly computed in the tyThingLocalGREs
function for a DataCon, as we were not taking into account other
DataCons with the same parent TyCon.

Fixes #23546