Fix slider notifies start and end twice when participates in gesture arena (#82152)

packages/flutter/lib/src/material/slider.dart

@@ -903,8 +903,7 @@ class _RenderSlider extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
     _tap = TapGestureRecognizer()
       ..team = team
       ..onTapDown = _handleTapDown
-      ..onTapUp = _handleTapUp
-      ..onTapCancel = _endInteraction;
+      ..onTapUp = _handleTapUp;
     _overlayAnimation = CurvedAnimation(
       parent: _state.overlayController,
       curve: Curves.fastOutSlowIn,
@@ -1224,7 +1223,7 @@ class _RenderSlider extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
 
   void _startInteraction(Offset globalPosition) {
     _state.showValueIndicator();
-    if (isInteractive) {
+    if (!_active && isInteractive) {
       _active = true;
       // We supply the *current* value as the start location, so that if we have
       // a tap, it consists of a call to onChangeStart with the previous value and

packages/flutter/test/material/slider_test.dart

@@ -908,6 +908,46 @@ void main() {
     await gesture.up();
   });
 
+  testWidgets('Slider onChangeStart and onChangeEnd fire once', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/28115
+
+    int startFired = 0;
+    int endFired = 0;
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Directionality(
+          textDirection: TextDirection.ltr,
+          child: Material(
+            child: Center(
+              child: GestureDetector(
+                onHorizontalDragUpdate: (_) { },
+                child: Slider(
+                  value: 0.0,
+                  onChanged: (double newValue) { },
+                  onChangeStart: (double value) {
+                    startFired += 1;
+                  },
+                  onChangeEnd: (double value) {
+                    endFired += 1;
+                  },
+                ),
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+
+    await tester.timedDrag(
+      find.byType(Slider),
+      const Offset(20.0, 0.0),
+      const Duration(milliseconds: 100),
+    );
+
+    expect(startFired, equals(1));
+    expect(endFired, equals(1));
+  });
+
   testWidgets('Slider sizing', (WidgetTester tester) async {
     await tester.pumpWidget(
       MaterialApp(