Add missing Str.substr(Any x) candidate
Add missing Str.substr(Any x) candidate

Fixes #1624, tests needed.

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