Unity scene view handles to rotate an object around a circle.

RotateAroundCircle.cs

using UnityEditor;
using UnityEditor.IMGUI.Controls;
using UnityEngine;

public class RotateAroundCircle : MonoBehaviour
{
    public Color color = Color.cyan;
    public Vector3 pivot;
}

[CustomEditor(typeof(RotateAroundCircle))]
public class RotateAroundCircleEditor : Editor
{
    ArcHandle handle;

    void OnEnable()
    {
        var targetComponent = target as RotateAroundCircle;

        if (targetComponent == null)
        {
            return;
        }

        handle = new ArcHandle();
        handle.SetColorWithoutRadiusHandle(targetComponent.color, 0);
        handle.wireframeColor = Color.clear;
    }

    void OnSceneGUI()
    {
        var targetComponent = target as RotateAroundCircle;

        if (targetComponent == null)
        {
            return;
        }

        var transform = targetComponent.transform;
        var position = transform.position;
        var levelPivot = new Vector3(targetComponent.pivot.x, position.y, targetComponent.pivot.z);
        var angle = Mathf.Atan2(position.x, position.z) * Mathf.Rad2Deg;
        var radius = Vector3.Distance(levelPivot, position);
        var matrix = Matrix4x4.TRS(levelPivot, Quaternion.identity, Vector3.one);

        handle.angle = angle;
        handle.radius = radius;

        using (new Handles.DrawingScope(targetComponent.color, matrix))
        {
            EditorGUI.BeginChangeCheck();
            handle.DrawHandle();

            if (EditorGUI.EndChangeCheck())
            {
                transform.RotateAround(levelPivot, Vector3.up, handle.angle - angle);
            }

            Handles.DrawWireDisc(Vector3.zero, Vector3.up, radius);
        }
    }
}