Hide utility class constructors

Update all utility classes so that they have a private constructor. This
prevents users from accidentally creating an instance, when they should
just use the static methods directly.

Issue gh-8945

ldap/src/main/java/org/springframework/security/ldap/ppolicy/PasswordPolicyControlExtractor.java

@@ -29,10 +29,13 @@ import org.apache.commons.logging.LogFactory;
  * @author Luke Taylor
  * @since 3.0
  */
-public class PasswordPolicyControlExtractor {
+public final class PasswordPolicyControlExtractor {
 
 	private static final Log logger = LogFactory.getLog(PasswordPolicyControlExtractor.class);
 
+	private PasswordPolicyControlExtractor() {
+	}
+
 	public static PasswordPolicyResponseControl extractControl(DirContext dirCtx) {
 		LdapContext ctx = (LdapContext) dirCtx;
 		Control[] ctrls = null;