8300177: URISyntaxException fields can be final

Reviewed-by: dfuchs, alanb, jpai

Author: DarraghClarke

src/java.base/share/classes/java/net/URISyntaxException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2023, 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
@@ -44,13 +44,13 @@ public class URISyntaxException
     /**
      * The input string.
      */
-    private String input;
+    private final String input;
 
     /**
      * The index at which the parse error occurred,
      * or {@code -1} if the index is not known.
      */
-    private int index;
+    private final int index;
 
     /**
      * Constructs an instance from the given input string, reason, and error