varnames(...) where each argument contains the name
of the variable at that offset. If the read Clause is a DCG rule,
name the two last arguments <DCG_list> and <DCG_tail>
This predicate calles the multifile predicate make_varnames_hook/5 with the same arguments to allow for user extensions. Extending this predicate is needed if a compiler adds additional arguments to the clause head that must be made visible in the GUI tracer.
| Offsets | - List of Offset=Var |
| Names | - List of Name=Var |