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

test/src/main/java/org/springframework/security/test/web/reactive/server/SecurityMockServerConfigurers.java

@@ -97,7 +97,10 @@ import org.springframework.web.server.adapter.WebHttpHandlerBuilder;
  * @author Rob Winch
  * @since 5.0
  */
-public class SecurityMockServerConfigurers {
+public final class SecurityMockServerConfigurers {
+
+	private SecurityMockServerConfigurers() {
+	}
 
 	/**
 	 * Sets up Spring Security's {@link WebTestClient} test support

test/src/main/java/org/springframework/security/test/web/servlet/setup/SecurityMockMvcConfigurers.java

@@ -30,6 +30,9 @@ import org.springframework.util.Assert;
  */
 public final class SecurityMockMvcConfigurers {
 
+	private SecurityMockMvcConfigurers() {
+	}
+
 	/**
 	 * Configures the MockMvcBuilder for use with Spring Security. Specifically the
 	 * configurer adds the Spring Bean named "springSecurityFilterChain" as a Filter. It