Add merge support to nested collection properties

Prior to this change, the merge attribute on nested collections was not
handled properly which would result in the typical replacement
behaviour. This is because during the merging of the parent and child
beans the parent bean would have nested BeanDefinition objects while the
child would have a property with the nested name
(beanA.beanB.propertyName). When it came time to look for matching the
property names it would be looking for the nested name which would not
exist in the parent.

The implementation of MutablePropertyValues.addProperty(PropertyValue)
will now try to find a chain of nested BeanDefinition objects that match
the nested property name and walk down the chain of beans and find the
property and then merge if applicable.

A JUnit test has been added to check for the new behaviour.

Issue: SPR-9552

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