Fix concurrency for StandardIntegrationFlowContext

If we don't get access to `BeanFactory` in exclusive mode,
the `getBean(Class<?>)` may fail with a `BeanCurrentlyInCreationException`
when we register several `IntegrationFlow` instances in parallel

Author: artembilan

spring-integration-core/src/main/java/org/springframework/integration/dsl/context/StandardIntegrationFlowContext.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2023 the original author or authors.
+ * Copyright 2016-2024 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.
@@ -95,11 +95,9 @@ public boolean isUseIdAsPrefix(String flowId) {
 	private IntegrationFlowRegistration register(StandardIntegrationFlowRegistrationBuilder builder) {
 		IntegrationFlow integrationFlow = builder.integrationFlow;
 		String flowId = builder.id;
-		Lock registerBeanLock = null;
+		this.registerFlowsLock.lock();
 		try {
 			if (flowId == null) {
-				registerBeanLock = this.registerFlowsLock;
-				registerBeanLock.lock();
 				flowId = generateBeanName(integrationFlow, null);
 				builder.id(flowId);
 			}
@@ -112,9 +110,7 @@ else if (this.registry.containsKey(flowId)) {
 			integrationFlow = registerFlowBean(integrationFlow, flowId, builder.source);
 		}
 		finally {
-			if (registerBeanLock != null) {
-				registerBeanLock.unlock();
-			}
+			this.registerFlowsLock.unlock();
 		}
 
 		builder.integrationFlow = integrationFlow;
@@ -209,7 +205,6 @@ private void removeDependantBeans(String parentName) {
 		for (String beanName : dependentBeans) {
 			removeDependantBeans(beanName);
 			this.beanDefinitionRegistry.removeBeanDefinition(beanName);
-			// TODO until https://jira.spring.io/browse/SPR-16837
 			String[] aliases = this.beanDefinitionRegistry.getAliases(beanName);
 			for (String alias : aliases) {
 				this.beanDefinitionRegistry.removeAlias(alias);