8325189: Enable this-escape javac warning in java.base

Reviewed-by: alanb, erikj, naoto, smarks, ihse, joehw, lancea, weijun

src/java.base/share/classes/java/io/ObjectOutputStream.java

@@ -246,6 +246,7 @@ public class ObjectOutputStream
      * @see     ObjectOutputStream#putFields()
      * @see     ObjectInputStream#ObjectInputStream(InputStream)
      */
+    @SuppressWarnings("this-escape")
     public ObjectOutputStream(OutputStream out) throws IOException {
         verifySubclass();
         bout = new BlockDataOutputStream(out);