Introduce MethodInvoker API for TestExecutionListeners

In order to be able to support parameter injection in
@​BeforeTransaction and @​AfterTransaction methods (see gh-30736), this
commit introduces a MethodInvoker API for TestExecutionListeners as a
generic mechanism for delegating to the underlying testing framework to
invoke methods.

The default implementation simply invokes the method without arguments,
which allows TestExecutionListeners using this mechanism to operate
correctly when the underlying testing framework is JUnit 4, TestNG, etc.

A JUnit Jupiter specific implementation is registered in the
SpringExtension which delegates to the
ExtensionContext.getExecutableInvoker() mechanism introduced in JUnit
Jupiter 5.9. This allows a TestExecutionListener to transparently
benefit from registered ParameterResolvers in JUnit Jupiter (including
the SpringExtension) when invoking user methods, effectively providing
support for parameter injection for arbitrary methods.

Closes gh-31199

spring-test/src/test/java/org/springframework/test/context/transaction/TransactionalTestExecutionListenerTests.java

@@ -37,6 +37,7 @@ import org.springframework.transaction.support.SimpleTransactionStatus;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
 import static org.mockito.BDDMockito.given;
+import static org.mockito.Mockito.CALLS_REAL_METHODS;
 import static org.mockito.Mockito.mock;
 import static org.springframework.transaction.annotation.Propagation.NOT_SUPPORTED;
 import static org.springframework.transaction.annotation.Propagation.REQUIRED;
@@ -58,7 +59,7 @@ class TransactionalTestExecutionListenerTests {
 		}
 	};
 
-	private final TestContext testContext = mock();
+	private final TestContext testContext = mock(CALLS_REAL_METHODS);
 
 
 	@AfterEach