8229997: Apply java.io.Serial annotations in java.base

Reviewed-by: alanb, rriggs

src/java.base/share/classes/java/util/regex/Pattern.java

@@ -935,6 +935,7 @@ public final class Pattern
      */
 
     /** use serialVersionUID from Merlin b59 for interoperability */
+    @java.io.Serial
     private static final long serialVersionUID = 5073258162644648461L;
 
     /**
@@ -1376,6 +1377,7 @@ public final class Pattern
      * Recompile the Pattern instance from a stream.  The original pattern
      * string is read in and the object tree is recompiled from it.
      */
+    @java.io.Serial
     private void readObject(java.io.ObjectInputStream s)
         throws java.io.IOException, ClassNotFoundException {
 

src/java.base/share/classes/java/util/regex/PatternSyntaxException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1999, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1999, 2019, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -37,6 +37,7 @@ package java.util.regex;
 public class PatternSyntaxException
     extends IllegalArgumentException
 {
+    @java.io.Serial
     private static final long serialVersionUID = -3864639126226059218L;
 
     private final String desc;