[kernel] Better printing of string and unevaluated constants.

This makes the printed constant pool easier to read.

Change-Id: I54d8223faeed9cb92454f4f0128f60b7e839ee42
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/96904
Reviewed-by: Kevin Millikin <kmillikin@google.com>
Commit-Queue: Aske Simon Christensen <askesc@google.com>
diff --git a/pkg/kernel/lib/text/ast_to_text.dart b/pkg/kernel/lib/text/ast_to_text.dart
index 5e7d228..29af291 100644
--- a/pkg/kernel/lib/text/ast_to_text.dart
+++ b/pkg/kernel/lib/text/ast_to_text.dart
@@ -2020,11 +2020,16 @@
     endLine(sb.toString());
   }
 
+  visitStringConstant(StringConstant node) {
+    final String name = syntheticNames.nameConstant(node);
+    endLine('  $name = "${escapeString(node.value)}"');
+  }
+
   visitUnevaluatedConstant(UnevaluatedConstant node) {
     final String name = syntheticNames.nameConstant(node);
-    write('  $name = ');
+    write('  $name = (');
     writeExpression(node.expression);
-    endLine();
+    endLine(')');
   }
 
   defaultNode(Node node) {