Lock range of range selector

When lock range is enabled, you can move both the thumbs at the same time by dragging in the area between start and end thumbs. It is false by default.

dart

final double _min = 2.0;
final double _max = 10.0;
SfRangeValues _values = SfRangeValues(4.0, 6.0);

final List<Data> chartData = <Data>[
    Data(x:2.0, y: 2.2),
    Data(x:3.0, y: 3.4),
    Data(x:4.0, y: 2.8),
    Data(x:5.0, y: 1.6),
    Data(x:6.0, y: 2.3),
    Data(x:7.0, y: 2.5),
    Data(x:8.0, y: 2.9),
    Data(x:9.0, y: 3.8),
    Data(x:10.0, y: 3.7),
];

@override
Widget build(BuildContext context) {
  return MaterialApp(
      home: Scaffold(
          body: Center(
              child: SfRangeSelector(
                    min: _min,
                    max: _max,
                    interval: 2,
                    showTicks: true,
                    showLabels: true,
                    initialValues: _values,
                    lockRange: true,
                    child: Container(
                    height: 130,
                    child: SfCartesianChart(
                        margin: const EdgeInsets.all(0),
                        primaryXAxis: NumericAxis(minimum: _min,
                            maximum: _max,
                            isVisible: false),
                        primaryYAxis: NumericAxis(isVisible: false),
                        plotAreaBorderWidth: 0,
                        series: <SplineAreaSeries<Data, double>>[
                            SplineAreaSeries<Data, double>(
                                color: Color.fromARGB(255, 126, 184, 253),
                                dataSource: chartData,
                                    xValueMapper: (Data sales, _) => sales.x,
                                    yValueMapper: (Data sales, _) => sales.y)
                            ],
                        ),
                   ),
              ),
          )
      )
  );
}

dart

class Data {
  Data({this.x, this.y});
  final double x;
  final double y;
}