Fix &list(Seq:D) to produce a List

Per #1344 , a Seq is not
a "list", because it does not do a Positional role.

src/core/List.pm

@@ -1535,7 +1535,8 @@ sub permutations(Int() $n) {
     Seq.new(Rakudo::Iterator.Permutations($n,0))
 }
 
-sub list(+l) { l }
+multi list(+l) { l }
+multi list(Seq:D \seq) { seq.list }
 
 # Use **@list and then .flat it, otherwise we'll end up remembering all the
 # things we flatten, which would be different semantics to .flat which gives