[FEATURE] Apply XPath query on current node

The XML-handling code is modified to allow for the execution
of the "xpath" property on the current node if the "field"
property is not defined.

On the side, the ChangeLog is updated for missing recent
updates.

Resolves: #51534
Releases: 2.3
Change-Id: I4a462b461c8f1d034c29582680e62310da590d38
Reviewed-on: https://review.typo3.org/29938
Reviewed-by: Francois Suter
Tested-by: Francois Suter