8029173: Debugger support doesn't handle ConsString

Reviewed-by: lagergren, hannesw, sundar

nashorn/src/jdk/nashorn/internal/runtime/DebuggerSupport.java

@@ -243,7 +243,7 @@ final class DebuggerSupport {
             return value.toString();
 
         case STRING:
-            return escape((String)value);
+            return escape(value.toString());
 
         case NUMBER:
             return JSType.toString(((Number)value).doubleValue());