Start expanding autocast during type resolution

Start expanding autocast during type resolution

There's no real propagation yet, so you can only try directly
transferred types so far, like:

  probe oneshot {
    println( (& @cast(task_current(), "task_struct")) ->pid )
  }

So that captures the task_current() address *with* the type, and then
the "->pid" is working as a separate expression to dereference it.

* elaborate.cxx (semantic_pass_symbols): Move build_no_more from here...
  (semantic_pass): ... to here, well after all types are resolved.
  (autocast_expanding_visitor): New, call on the type_details to expand
  autocast_op into a functioncall, like any $var/@cast would.
  (semantic_pass_types): Use autocast_expanding_visitor whenever the
  normal type resolution indicated there might be something to do.
  (typeresolution_info::visit_autocast_op):  Don't fail immediately;
  just visit the operand, and note when type_details show up.
* tapsets.cxx (exp_type_dwarf::expand): Expand that autocast_op!
  (dwarf_autocast_expanding_visitor): Removed in favor of just having
  autocast_expanding_visitor call exp_type_ptr->expand().