Summary:
A DropArea has been added to the ListItem representing a device in the
plasmoid based on what is done in the Quickshare plasmoid. This enables
Drag n Drop of files onto a section of the plasmoid to transfer files.

The DropArea has the size of the ListItem which is a rectangle
including the title of the device down to the button to share text.
Additionally, there is a tooltip area covering the DropArea to indicate
that it is possible to drop a file to send it to the device. Multiple files
can be sent at once.

Ref T8288

Test Plan: Drag and Drop one or many files onto the widget, the files should be transferred to the connected device.

Reviewers: #kde_connect, sredman

Reviewed By: #kde_connect, sredman

Subscribers: sredman, kdeconnect

Tags: #kde_connect

Maniphest Tasks: T8288

Differential Revision: https://phabricator.kde.org/D17611