This commit allows to set the XmlBeanDefinitionReader field from
BeanDefinitionLoader to null in a way that allows the GraalVM native
compiler to remove it from the native image when the spring.xml.ignore
flag introduced by spring-projects/spring-framework#25151
is set to true.
The purpose of this change is to allow smaller footprint on native
images without requiring to use GraalVM native substitutions
which are unmaintainable by nature and also to increase the consistency
between JVM and native images.
In order to effective, this optimization requires BeanDefinitionLoader
class to be initialized at build time.
See gh-22093
8d5cf79675