RakuAST: add RakuAST::Literal.new

This will look at the type of the value passed and create the
appropriate object.  E.g. RakuAST::Literal.new(42) will create
a RakuAST::IntLiteral because 42 is an Int.

This should make manual building of ASTs simpler.

src/Raku/ast/literals.rakumod

@@ -14,6 +14,11 @@ class RakuAST::Literal
         $context.ensure-sc($value);
         QAST::WVal.new( :$value )
     }
+
+    method new(Mu $value) {
+        my $type := $value.HOW.name($value) ~ 'Literal';
+        RakuAST.WHO{$type}.new($value)
+    }
 }
 
 class RakuAST::IntLiteral