[perl #77680] perlsub pointers to sub names used by perl itself

Tony Cook: convert from a diff to a commit
test and briefly document DB::goto
briefly document DB::lsub
[perl #77680] add pointers to a few other perl called subs
[perl #77680] document list of special subs in perlsub

This also adds documentation for the undocumented DB::goto and
DB::lsub.