[Debug] Improve readability of positioninfo debug format

Summary:
The docId in hex is shorter and can be better compared with the
serialized data. Also remove extra whitespace.

No functional changes.

Reviewers: Baloo, ngraham

Reviewed By: Baloo, ngraham

Subscribers: kde-frameworks-devel

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D27855