Add metadata about the changed value to a PROPERTY_CHANGED event on a multivalued property

When getting PROPERTY_CHANGED events on non-multivalued properties only one value can have actually changed so that handlers of such events do not need any further information to process it and eventually work on the changed value; on the other hand PROPERTY_CHANGED events on multivalued properties (e.g. String[]) may relate to any of the values and that brings a source of uncertainty on event handlers processing such changes because there's no mean to understand which property value had been changed and therefore to them to react accordingly.
A workaround for that is to create Oak specific Observers which can deal with the diff between before and after state and create a specific event containing the "diff", however this would add a non trivial load to the repository because of the Observer itself and because of the additional events being generated while it'd be great if the 'default' events would have metadata e.g. of the changed value index or similar information that can help understanding which value has been changed (added, deleted, updated).