notifications: When doing a drag and drop, set the supported action to cpoy
By default QDrag::exec performs a drag where the allowed actions are only "move".
The mimedata for a screenshot is a URI list to the file, dragging and dropping should not move the original file.
Equally importantly if we want to share a file, that's effectively a copy. Some clients will rightfully not accept a URI list with the only action being move.
Testing done:
Screenshot taken with the spectacle global shortcut, then drag from that into the Electron app "Discord"
Edited by David Edmundson