[Notifications] Implement JobViewV3

This implements a new JobViewV3 which uses extensible variant maps rather than individual function calls,
allowing for compression of calls and extensibility.
The new API uses infoMessage correctly as a state message, e.g. "Connecting to host" rather than mixing it with the "Copying..." heading.
It also supports an "immediate" flag that the caller can use to indicate progress should be immediately shown,
so in cases where the user is likely to want to use the file afterwards (e.g. download through p-b-i or receiving a file
through KDE Connect) a job popup is shown even for small/short transfers.

Differential Revision: https://phabricator.kde.org/D23293