[DynInst_API:] [dyninst/dyninst] 88018f: Make a default module a class invariant

[Tim Haines <noreply@xxxxxxxxxx>]

  Branch: refs/heads/thaines/symtab_default_module_invariant
  Home:   https://github.com/dyninst/dyninst
  Commit: 88018ff80d9c445f36ab1643ca80e29b948e1a32
      https://github.com/dyninst/dyninst/commit/88018ff80d9c445f36ab1643ca80e29b948e1a32
  Author: Tim Haines <thaines.astro@xxxxxxxxx>
  Date:   2023-09-27 (Wed, 27 Sep 2023)

  Changed paths:
    M symtabAPI/src/Symtab-lookup.C
    M symtabAPI/src/Symtab.C
    M symtabAPI/src/symtab_impl.hpp

  Log Message:
  -----------
  Make a default module a class invariant

This simplifies the handling of modules and ensures a default always
exists. Creation must happen after the MappedFile has been created, but
before the symbols are assigned to a Module.