Add EmptyLineSeparator Checkstyle rule

* Support "blank lines around" via `spring-framework.xml` IDEA config
* Fix all the Checkstyle violations

spring-integration-test/src/test/java/org/springframework/integration/test/mock/MockMessageHandlerTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2023 the original author or authors.
+ * Copyright 2017-2024 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.
@@ -211,7 +211,6 @@ public class MockMessageHandlerTests {
 				mockMessageHandler()
 						.handleNextAndReply(m -> m);
 
-
 		assertThatIllegalStateException()
 				.isThrownBy(() ->
 						this.mockIntegrationContext.substituteMessageHandlerFor(endpointId, mockMessageHandler2))
@@ -272,7 +271,6 @@ public class MockMessageHandlerTests {
 				.isSameAs(mockMessageHandler);
 	}
 
-
 	@Autowired
 	private MessageChannel reactiveInputChannel;
 
@@ -290,7 +288,6 @@ public class MockMessageHandlerTests {
 		verify(mockMessageHandler).handleMessage(any(Message.class));
 	}
 
-
 	@Configuration
 	@EnableIntegration
 	public static class Config {
@@ -361,7 +358,6 @@ public class MockMessageHandlerTests {
 			return new LoggingHandler(LoggingHandler.Level.FATAL);
 		}
 
-
 		@Bean
 		@EndpointId("reactiveEndpoint")
 		@ServiceActivator(inputChannel = "reactiveInputChannel", reactive = @Reactive)