Fix handling of generics in TypedArray.raku

Using TValue directly can lead to an attempt to call .raku on an
uninstantiated generic. Just use the type name of self instead of
building it with "Array" and TValue.

Fixes #3784

src/core.c/TypedArray.pm6

@@ -104,12 +104,12 @@
             )
         }
 
-        multi method raku(::?CLASS:D \SELF:) {
-            my $type := TValue.raku;
+        multi method raku(::?CLASS:D:) {
+            my $type := self.^name;
             my $raku := self.map({
                 nqp::isconcrete($_) ?? .raku(:arglist) !! $type
             }).join(', ');
-            'Array[' ~ $type ~ '].new(' ~ $raku ~ ')';
+            $type ~ '.new(' ~ $raku ~ ')'
         }
     }
     method ^parameterize(Mu:U \arr, Mu \t, |c) {