Replaced the repeated application of Cursors (Sphere or Circle) in painting using 2D and 3D Capsules.

Previously, the Cursor (Sphere or Circle) was repeatedly applied between two mouse positions, creating brushstrokes with ripples on the edges between those mouse positions.
Now, a single capsule (3D or 2D) is applied between those mouse positions, which creates brushstrokes without these ripples.

src/slic3r/GUI/MeshUtils.cpp

@@ -304,7 +304,13 @@ Vec3f MeshRaycaster::get_closest_point(const Vec3f& point, Vec3f* normal) const
     return closest_point.cast<float>();
 }
 
-
+int MeshRaycaster::get_closest_facet(const Vec3f &point) const
+{
+    int   facet_idx = 0;
+    Vec3d closest_point;
+    m_emesh.squared_distance(point.cast<double>(), facet_idx, closest_point);
+    return facet_idx;
+}
 
 } // namespace GUI
 } // namespace Slic3r