Use Bool() on postcircumfix:<[ ]> adverbs params
Use Bool() on postcircumfix:<[ ]> adverbs params

Saves one Scalar allocation per @foo[bar]:exists and the like.
Inspired by 74b755992d7d43e2feb5d

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