Cache CGLIB proxy classes properly again

The introduction of AdvisedSupport.AdvisorKeyEntry in Spring Framework
6.0.10 resulted in a regression regarding caching of CGLIB generated
proxy classes. Specifically, equality checks for the proxy class cache
became based partially on identity rather than equivalence. For
example, if an ApplicationContext was configured to create a
class-based @Transactional proxy, a second attempt to create the
ApplicationContext resulted in a duplicate proxy class for the same
@Transactional component.

On the JVM this went unnoticed; however, when running Spring
integration tests within a native image, if a test made use of
@⁠DirtiesContext, a second attempt to create the test
ApplicationContext resulted in an exception stating, "CGLIB runtime
enhancement not supported on native image." This is because Test AOT
processing only refreshes a test ApplicationContext once, and the
duplicate CGLIB proxy classes are only requested in subsequent
refreshes of the same ApplicationContext which means that duplicate
proxy classes are not tracked during AOT processing and consequently
not included in a native image.

This commit addresses this regression as follows.

- AdvisedSupport.AdvisorKeyEntry is now based on the toString()
  representations of the ClassFilter and MethodMatcher in the
  corresponding Pointcut instead of the filter's and matcher's
  identities.

- Due to the above changes to AdvisorKeyEntry, ClassFilter and
  MethodMatcher implementations are now required to implement equals(),
  hashCode(), AND toString().

- Consequently, the following now include proper equals(), hashCode(),
  and toString() implementations.

  - CacheOperationSourcePointcut
  - TransactionAttributeSourcePointcut
  - PerTargetInstantiationModelPointcut

Closes gh-31238

spring-tx/src/test/java/org/springframework/transaction/annotation/EnableTransactionManagementTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -69,6 +69,25 @@ public class EnableTransactionManagementTests {
 		ctx.close();
 	}
 
+	@Test  // gh-31238
+	public void cglibProxyClassIsCachedAcrossApplicationContexts() {
+		ConfigurableApplicationContext ctx;
+
+		// Round #1
+		ctx = new AnnotationConfigApplicationContext(EnableTxConfig.class, TxManagerConfig.class);
+		TransactionalTestBean bean1 = ctx.getBean(TransactionalTestBean.class);
+		assertThat(AopUtils.isCglibProxy(bean1)).as("testBean #1 is not a CGLIB proxy").isTrue();
+		ctx.close();
+
+		// Round #2
+		ctx = new AnnotationConfigApplicationContext(EnableTxConfig.class, TxManagerConfig.class);
+		TransactionalTestBean bean2 = ctx.getBean(TransactionalTestBean.class);
+		assertThat(AopUtils.isCglibProxy(bean2)).as("testBean #2 is not a CGLIB proxy").isTrue();
+		ctx.close();
+
+		assertThat(bean1.getClass()).isSameAs(bean2.getClass());
+	}
+
 	@Test
 	public void transactionProxyIsCreatedWithEnableOnSuperclass() {
 		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(