Show more details in warning dialog shown before starting a privileged operation

Summary:
Currently it uses the dialog from D21782 to provide the current action being performed, the source file and any
action specific detail.

The initial plan was to show all the files needing elevated privileges but due to KIO jobs processing one file at
a time only limited info could be provided. There's also the option for determing this during the stat phase but it
caused my VM to slow down to a crawl. Any more ideas here?

Reviewers: VDG, Frameworks, dfaure

Reviewed By: VDG, dfaure

Subscribers: mreeves, ngraham, kde-frameworks-devel

Tags: Frameworks

Maniphest Tasks: T8075

Differential Revision: https://phabricator.kde.org/D21783