Add "maint canonicalize" command

This adds a new "maint canonicalize" command that can be used to see
the canonical form of a C++ name.  I've needed this a few times when
debugging gdb.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Reviewed-By: Tom de Vries <tdevries@suse.de>
4 files changed