dnd_drop_zone changes style of widget even when nothing is being dragged

[JoshMcguigan]

Describe the bug

Drawing a widget within dnd_drop_zone draws a frame of the color defined in ui.visuals.widgets.inactive.bg_fill over the widget. This means a widget drawn in a drop zone looks different from a widget that is not in a drop zone.

I do think its desirable for the drop zone to be highlighted when active, but I don't think it should be highlighted when nothing is being dragged.

https://docs.rs/egui/0.30.0/src/egui/ui.rs.html#2832

^ This line ultimately leads to the inactive style being applied if nothing is being dragged.

Expected behavior

I expect a widget drawn inside of a drop zone look the same as a widget drawn not inside of a drop zone, until something is being dragged.

Additional context

I was able to work around this by setting the inactive.bg_fill to transparent, as in ui.visuals_mut().widgets.inactive.bg_fill = egui::Color32::TRANSPARENT;, but this is not a good solution because the docs say bg_fill should not be set to TRANSPARENT and also because other parts of the UI may have a valid use for inactive.bg_fill which I'd be breaking.