Spring Use MergedAnnotations API directly in AnnotationBeanNameGenerator where possible

AnnotationBeanNameGenerator was written before the introduction of the MergedAnnotations API and therefore heavily relies on the AnnotationMetadata abstraction and various helper methods for ASM compatibility.

However, recent work on determineBeanNameFromAnnotation(AnnotatedBeanDefinition) has made it apparent that we should use the MergedAnnotations API directly in AnnotationBeanNameGenerator where possible in order to avoid unnecessary, repeated iterations/streams over the same annotation metadata.