Migrating old Gallery to new Slider (#55201)

dev/integration_tests/flutter_gallery/lib/demo/material/expansion_panels_demo.dart

@@ -305,6 +305,7 @@ class _ExpansionPanelsDemoState extends State<ExpansionPanelsDemo> {
                         // Allow room for the value indicator.
                         padding: const EdgeInsets.only(top: 44.0),
                         child: Slider(
+                          useV2Slider: true,
                           min: 0.0,
                           max: 100.0,
                           divisions: 5,

dev/integration_tests/flutter_gallery/lib/demo/material/slider_demo.dart

@@ -274,6 +274,7 @@ class _SlidersState extends State<_Sliders> {
                 ),
               ),
               Slider.adaptive(
+                useV2Slider: true,
                 label: _continuousValue.toStringAsFixed(6).toString(),
                 value: _continuousValue,
                 min: 0.0,
@@ -290,7 +291,7 @@ class _SlidersState extends State<_Sliders> {
           Column(
             mainAxisSize: MainAxisSize.min,
             children: const <Widget>[
-              Slider.adaptive(value: 0.25, onChanged: null),
+              Slider.adaptive(useV2Slider: true, value: 0.25, onChanged: null),
               Text('Disabled'),
             ],
           ),
@@ -298,6 +299,7 @@ class _SlidersState extends State<_Sliders> {
             mainAxisSize: MainAxisSize.min,
             children: <Widget>[
               Slider.adaptive(
+                useV2Slider: true,
                 value: _discreteValue,
                 min: 0.0,
                 max: 200.0,
@@ -329,6 +331,7 @@ class _SlidersState extends State<_Sliders> {
                   valueIndicatorTextStyle: theme.accentTextTheme.bodyText1.copyWith(color: theme.colorScheme.onSurface),
                 ),
                 child: Slider(
+                  useV2Slider: true,
                   value: _discreteCustomValue,
                   min: 0.0,
                   max: 200.0,
@@ -372,6 +375,7 @@ class _RangeSlidersState extends State<_RangeSliders> {
             mainAxisSize: MainAxisSize.min,
             children: <Widget>[
               RangeSlider(
+                useV2Slider: true,
                 values: _continuousValues,
                 min: 0.0,
                 max: 100.0,
@@ -387,7 +391,7 @@ class _RangeSlidersState extends State<_RangeSliders> {
           Column(
             mainAxisSize: MainAxisSize.min,
             children: <Widget>[
-              RangeSlider(values: const RangeValues(0.25, 0.75), onChanged: null),
+              RangeSlider(useV2Slider: true, values: const RangeValues(0.25, 0.75), onChanged: null),
               const Text('Disabled'),
             ],
           ),
@@ -395,6 +399,7 @@ class _RangeSlidersState extends State<_RangeSliders> {
             mainAxisSize: MainAxisSize.min,
             children: <Widget>[
               RangeSlider(
+                useV2Slider: true,
                 values: _discreteValues,
                 min: 0.0,
                 max: 200.0,
@@ -424,6 +429,7 @@ class _RangeSlidersState extends State<_RangeSliders> {
                   showValueIndicator: ShowValueIndicator.never,
                 ),
                 child: RangeSlider(
+                  useV2Slider: true,
                   values: _discreteCustomValues,
                   min: 0.0,
                   max: 200.0,