Create empty EnumSets & EnumMaps in CollectionFactory

SPR-12483 introduced automatic type conversion support for EnumSet and
EnumMap. However, the corresponding changes in CollectionFactory
contradict the existing contract for the "create approximate" methods
by creating a copy of the supplied set or map, thereby potentially
including elements in the returned collection when the returned
collection should in fact be empty.

This commit addresses this issue by ensuring that the collections
returned by createApproximateCollection() and createApproximateMap()
are always empty.

Furthermore, this commit improves the Javadoc throughout the
CollectionFactory class.

Issue: SPR-12533