GH-3875: Initialize ClassUtils as early as possible

Fixes #3875

The class `static` variables and initialization block are performed on first class access.

* Add "fake" `ClassUtils.resolvePrimitiveType(Integer.class)` call to the `IntegrationRegistrar`
to trigger `ClassUtils` initialization with the current Spring `ClassLoader`

**Cherry-pick to `5.5.x`**

Author: artembilan

spring-integration-core/src/main/java/org/springframework/integration/config/IntegrationRegistrar.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2021 the original author or authors.
+ * Copyright 2014-2022 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.
@@ -56,6 +56,9 @@ public class IntegrationRegistrar implements ImportBeanDefinitionRegistrar {
 	public void registerBeanDefinitions(@Nullable AnnotationMetadata importingClassMetadata,
 			BeanDefinitionRegistry registry) {
 
+		// Ensure that ClassUtils is initialized with a proper Spring application context ClassLoader.
+		org.springframework.integration.util.ClassUtils.resolvePrimitiveType(Integer.class);
+
 		registerDefaultConfiguringBeanFactoryPostProcessor(registry);
 		registerIntegrationConfigurationBeanFactoryPostProcessor(registry);
 		if (importingClassMetadata != null) {