8305206: Add @spec tags in java.base/java.* (part 1)

Reviewed-by: alanb, naoto, darcy, lancea, dfuchs, iris, mchung

src/java.base/share/classes/java/lang/Enum.java

@@ -61,6 +61,8 @@ import static java.util.Objects.requireNonNull;
  * java.util.EnumMap map} implementations are available.
  *
  * @param <E> The type of the enum subclass
+ *
+ * @spec serialization/index.html Java Object Serialization Specification
  * @serial exclude
  * @author  Josh Bloch
  * @author  Neal Gafter