Consolidate print_format creation

Consolidate print_format creation

We almost had a factory in print_format::parse_print, so let's take that
the rest of the way.  This way we don't have so much duplication in
initializing the print flags.

* staptree.cxx (print_format::parse_print): Replaced with...
  (print_format::create): New factory to parse and create print_formats.
* elaborate.cxx (add_global_var_display): Use this factory.
* parse.cxx (parser::parse_symbol): Ditto.
* tapset-mark.cxx
  (mark_var_expanding_visitor::visit_target_symbol_context): Ditto.
* tapset-utrace.cxx
  (utrace_var_expanding_visitor::visit_target_symbol_arg): Ditto.
* tapsets.cxx
  (dwarf_var_expanding_visitor::visit_target_symbol_context): Ditto.
  (tracepoint_var_expanding_visitor::visit_target_symbol_context) Ditto.