Add move semantics support to KIO::UDSEntry.

Summary:
Adds move semantics support and a testcase (only useful in callgrind).
Right now there are 0 uses of these semantics.

Test Plan:
Relevant tests (udsentrytest and kfileitemtest) pass.
Dolphin compiles and runs just fine with it.

Reviewers: dfaure

Subscribers: apol, Frameworks

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D10414