Array.ASSIGN-POS 4x faster for unreified elements
Array.ASSIGN-POS 4x faster for unreified elements

- and 10% faster for reified elements
- drop the SLOW-PATH altogether
- don't allocate unless we must
- 7 allocations less per assignment for unreified
- 1 allocation less for assignment to reified

lucasbuchala/rakudo,MasterDuke17/rakudo,jonathanstowe/rakudo,softmoth/rakudo,usev6/rakudo,awwaiid/rakudo,usev6/rakudo,rakudo/rakudo,nbrown/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,softmoth/rakudo,zostay/rakudo,salortiz/rakudo,tbrowder/rakudo,labster/rakudo,samcv/rakudo,labster/rakudo,zostay/rakudo,usev6/rakudo,awwaiid/rakudo,tbrowder/rakudo,nbrown/rakudo,nbrown/rakudo,sjn/rakudo,Gnouc/rakudo,rakudo/rakudo,salortiz/rakudo,tony-o/rakudo,awwaiid/rakudo,raydiak/rakudo,rakudo/rakudo,usev6/rakudo,zostay/rakudo,tbrowder/rakudo,Gnouc/rakudo,MasterDuke17/rakudo,sjn/rakudo,MasterDuke17/rakudo,lucasbuchala/rakudo,nbrown/rakudo,awwaiid/rakudo,sjn/rakudo,tony-o/rakudo,raydiak/rakudo,lucasbuchala/rakudo,rakudo/rakudo,samcv/rakudo,jonathanstowe/rakudo,Gnouc/rakudo,salortiz/rakudo,usev6/rakudo,sjn/rakudo,samcv/rakudo,samcv/rakudo,zostay/rakudo,salortiz/rakudo,softmoth/rakudo,tbrowder/rakudo,labster/rakudo,tony-o/rakudo,rakudo/rakudo,samcv/rakudo,salortiz/rakudo,tony-o/rakudo,lucasbuchala/rakudo,MasterDuke17/rakudo,salortiz/rakudo,labster/rakudo,lucasbuchala/rakudo,labster/rakudo,jonathanstowe/rakudo,Gnouc/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,raydiak/rakudo,softmoth/rakudo,raydiak/rakudo,awwaiid/rakudo,jonathanstowe/rakudo,nbrown/rakudo,rakudo/rakudo,sjn/rakudo,jonathanstowe/rakudo,tony-o/rakudo,labster/rakudo,tony-o/rakudo,nbrown/rakudo,Gnouc/rakudo,Gnouc/rakudo,softmoth/rakudo