Limit variable layer height displaying precision to 3 digits (#5795)

* Limit variable layer height calculation and displaying precision to three digits.

* Remove calculation rounding.

src/slic3r/GUI/GLCanvas3D.cpp

@@ -383,7 +383,7 @@ std::string GLCanvas3D::LayersEditing::get_tooltip(const GLCanvas3D& canvas) con
                 }
             }
             if (h > 0.0f)
-                ret = std::to_string(h);
+                ret = wxString::Format("%.3f",h).ToStdString();
         }
     }
     return ret;