Summary: Add KListOpenFilesJob for retrieving the list of processes that have opened files in the given path or a subdirectory of path. This code is ported from Device Notifier but rewritten to use KJob.
Test Plan: Unit Tests
Reviewed By: dfaure
Subscribers: meven, cfeck, kde-frameworks-devel
Differential Revision: https://phabricator.kde.org/D21760