Interactive rounded gizmos at polyline corners

It is recommended to add a rounded corner icon to polygons. This icon should be displayed when a polygon is selected. Clicking the icon should navigate to the "Corner Radius" settings panel, and it should also allow for dragging to create rounded corners, as shown in the image.

Start by locating the polygon-selection controls and the existing "Corner Radius" settings panel, then compare them with the interaction shown in the attached image. The feature is done when a selected polygon shows a rounded-corner gizmo, clicking it opens the panel, and dragging it creates rounded corners.

Written by the indexing model from the issue text.