optimizer: consider more kinds of symbol "present"
optimizer: consider more kinds of symbol "present"

when checking if something comes from the core or has
been overwritten locally; maybe the introduction
of nested cores or something else made lots of
operators and other subs have only "lazy_value_from"
and "scope" keys in their symbol table entry. Until
now only the presence of a "value" entry was enough
to consider a symbol "present".

salortiz/rakudo,nbrown/rakudo,MasterDuke17/rakudo,tony-o/rakudo,labster/rakudo,rakudo/rakudo,tony-o/rakudo,MasterDuke17/rakudo,labster/rakudo,tbrowder/rakudo,softmoth/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,tony-o/rakudo,MasterDuke17/rakudo,salortiz/rakudo,tony-o/rakudo,softmoth/rakudo,rakudo/rakudo,labster/rakudo,nbrown/rakudo,softmoth/rakudo,tony-o/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,tony-o/rakudo,salortiz/rakudo,nbrown/rakudo,MasterDuke17/rakudo,rakudo/rakudo,tbrowder/rakudo,labster/rakudo,rakudo/rakudo,tbrowder/rakudo,rakudo/rakudo,salortiz/rakudo,nbrown/rakudo,nbrown/rakudo,softmoth/rakudo,salortiz/rakudo,nbrown/rakudo,softmoth/rakudo,salortiz/rakudo,tbrowder/rakudo,rakudo/rakudo,labster/rakudo,labster/rakudo