Stateless, synchronized draggable elements

[cyyynthia]

Is your feature request related to a problem? Please describe.
Draggable elements are mostly a way to have floating elements on the slides, however I found them to be valuable as a tool to make interactive visual demonstrations, dragging elements around while speaking.

It is however, as it's initially a slide design tool, stateful and will write back the new coordinates to the slide file (which is pretty minor), but most importantly is not synced across the presenter and play views.

Describe the solution you'd like
Have the draggable elements be synced across views. Bonus points if they can be made stateless, such that moving them around doesn't save a new position to the slides file.

Describe alternatives you've considered
Screen mirroring has been added recently (see #1987) but has trade-offs, most notably when dealing with multi-device seups.

See also #1987 (comment)