[UDisks2] Power down drive on remove if supported

Summary:
It is preferable to to do a controlled shutdown prior to disconnecting
and eventually cutting of power to the drive.

BUG: 270808
Closes T9730

Test Plan:
Connect external drive, select "Savely Remove" from context menu

1. if drive has only on partition, fs is unmounted and drive spins down
2. if drive has multiple partitions: a) first (not last) partition can be unmounted and remounted b) "Remove"ing last partition spins down drive

Reviewers: Frameworks, ngraham, broulik

Reviewed By: ngraham, broulik

Subscribers: broulik, kde-frameworks-devel, ngraham

Tags: Frameworks

Maniphest Tasks: T9730

Differential Revision: https://phabricator.kde.org/D15932