RakuAST: dump post processors on quoted strings as extras

Post processors have significant impact on the generated code and this
code's result, so include information about them in the AST dump output.

src/Raku/ast/literals.rakumod

@@ -312,6 +312,12 @@ class RakuAST::QuotedString is RakuAST::ColonPairish is RakuAST::Term
         False
     }
 
+    method dump-extras(int $indent) {
+        $!processors && nqp::elems($!processors)
+            ?? nqp::x(' ', $indent) ~ 'postprocessors: ' ~ nqp::join(', ', $!processors) ~ "\n"
+            !! ''
+    }
+
     method IMPL-EXPR-QAST(RakuAST::IMPL::QASTContext $context) {
         # If we can constant fold it, just produce the constant.
         my $literal-value := self.literal-value;