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

core/src/test/java/org/springframework/security/access/annotation/sec2150/MethodInvocationFactory.java

@@ -19,7 +19,10 @@ package org.springframework.security.access.annotation.sec2150;
 import org.springframework.aop.framework.ProxyFactory;
 import org.springframework.security.access.intercept.method.MockMethodInvocation;
 
-public class MethodInvocationFactory {
+public final class MethodInvocationFactory {
+
+	private MethodInvocationFactory() {
+	}
 
 	/**
 	 * In order to reproduce the bug for SEC-2150, we must have a proxy object that

core/src/test/java/org/springframework/security/access/expression/method/SecurityRules.java

@@ -16,7 +16,10 @@
 
 package org.springframework.security.access.expression.method;
 
-public class SecurityRules {
+public final class SecurityRules {
+
+	private SecurityRules() {
+	}
 
 	public static boolean disallow() {
 		return false;

core/src/test/java/org/springframework/security/util/FieldUtilsTests.java

@@ -27,8 +27,6 @@ public class FieldUtilsTests {
 
 	@Test
 	public void gettingAndSettingProtectedFieldIsSuccessful() throws Exception {
-		new FieldUtils();
-
 		Object tc = new TestClass();
 
 		assertThat(FieldUtils.getProtectedFieldValue("protectedField", tc)).isEqualTo("x");

core/src/test/java/org/springframework/security/util/MethodInvocationUtilsTests.java

@@ -33,8 +33,6 @@ public class MethodInvocationUtilsTests {
 
 	@Test
 	public void createFromClassReturnsMethodWithNoArgInfoForMethodWithNoArgs() {
-		new MethodInvocationUtils();
-
 		MethodInvocation mi = MethodInvocationUtils.createFromClass(String.class, "length");
 		assertThat(mi).isNotNull();
 	}