8231186: Replace html tag <code>foo</code> with javadoc tag {@code foo} in java.base

Minor coding style update of javadoc tag in any file in java.base

Reviewed-by: bchristi, lancea

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

@@ -164,7 +164,7 @@ public class OutputStreamWriter extends Writer {
      * been closed. </p>
      *
      * @return The historical name of this encoding, or possibly
-     *         <code>null</code> if the stream has been closed
+     *         {@code null} if the stream has been closed
      *
      * @see java.nio.charset.Charset
      *