Dashboard: optionally show drop-areas in all slots when dragging

[rolfsmeds]

Describe your motivation

When dragging an item in the Dashboard, it currently only renders a drop-indicator at the location where the widget would drop if released at that moment:

This can confuse users who don't realize that other possible drop-locations are available.

Describe the solution you'd like

When a drag-and-drop is happening, the Dashboard could render potential-drop-target indicators in all locations where a drop can be made, e.g. something along the lines of this:

This could be an opt-in feature.

Describe alternatives you've considered

No response

Additional context

No response