Add FocusNode, onFocusChange, and autofocus to CupertinoSwitch (#126684)

fixes flutter/flutter#126679 

### Description
Control cupertino widgets like `CupertinoCheckbox` and `CupertinoRadio` have `focusNode` and `autofocus`, while these are missing in `CupertinoSwitch`.

This is blocking flutter/flutter#126637 
(`switch.dart` currently maintains its focus node for `CupertinoSwitch` when using `Switch.adaptive` which causes a bug)

Author: TahaTesser

packages/flutter/lib/src/cupertino/switch.dart

@@ -75,6 +75,9 @@ class CupertinoSwitch extends StatefulWidget {
     this.thumbColor,
     this.applyTheme,
     this.focusColor,
+    this.focusNode,
+    this.onFocusChange,
+    this.autofocus = false,
     this.dragStartBehavior = DragStartBehavior.start,
   });
 
@@ -130,6 +133,15 @@ class CupertinoSwitch extends StatefulWidget {
   /// Defaults to a slightly transparent [activeColor].
   final Color? focusColor;
 
+  /// {@macro flutter.widgets.Focus.focusNode}
+  final FocusNode? focusNode;
+
+  /// {@macro flutter.material.inkwell.onFocusChange}
+  final ValueChanged<bool>? onFocusChange;
+
+  /// {@macro flutter.widgets.Focus.autofocus}
+  final bool autofocus;
+
   /// {@template flutter.cupertino.CupertinoSwitch.applyTheme}
   /// Whether to apply the ambient [CupertinoThemeData].
   ///
@@ -356,6 +368,9 @@ class _CupertinoSwitchState extends State<CupertinoSwitch> with TickerProviderSt
           onShowFocusHighlight: _onShowFocusHighlight,
           actions: _actionMap,
           enabled: isInteractive,
+          focusNode: widget.focusNode,
+          onFocusChange: widget.onFocusChange,
+          autofocus: widget.autofocus,
           child: _CupertinoSwitchRenderObjectWidget(
             value: widget.value,
             activeColor: activeColor,

packages/flutter/test/cupertino/switch_test.dart

@@ -913,4 +913,115 @@ void main() {
       kIsWeb ? SystemMouseCursors.click : SystemMouseCursors.basic,
     );
   });
+
+  testWidgets('CupertinoSwitch is focusable and has correct focus color', (WidgetTester tester) async {
+    final FocusNode focusNode = FocusNode(debugLabel: 'CupertinoSwitch');
+    tester.binding.focusManager.highlightStrategy = FocusHighlightStrategy.alwaysTraditional;
+    bool value = true;
+    const Color focusColor = Color(0xffff0000);
+
+    Widget buildApp({bool enabled = true}) {
+      return Directionality(
+        textDirection: TextDirection.ltr,
+        child: StatefulBuilder(
+          builder: (BuildContext context, StateSetter setState) {
+            return Center(
+              child: CupertinoSwitch(
+                value: value,
+                onChanged: enabled ? (bool newValue) {
+                  setState(() {
+                    value = newValue;
+                  });
+                } : null,
+                focusColor: focusColor,
+                focusNode: focusNode,
+                autofocus: true,
+              ),
+            );
+          },
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildApp());
+    await tester.pumpAndSettle();
+
+    expect(focusNode.hasPrimaryFocus, isTrue);
+    expect(
+      find.byType(CupertinoSwitch),
+      paints
+        ..rrect(color: const Color(0xff34c759))
+        ..rrect(color: focusColor)
+        ..clipRRect()
+        ..rrect(color: const Color(0x26000000))
+        ..rrect(color: const Color(0x0f000000))
+        ..rrect(color: const Color(0x0a000000))
+        ..rrect(color: const Color(0xffffffff)),
+    );
+
+    // Check the false value.
+    value = false;
+    await tester.pumpWidget(buildApp());
+    await tester.pumpAndSettle();
+
+    expect(focusNode.hasPrimaryFocus, isTrue);
+    expect(
+      find.byType(CupertinoSwitch),
+      paints
+        ..rrect(color: const Color(0x28787880))
+        ..rrect(color: focusColor)
+        ..clipRRect()
+        ..rrect(color: const Color(0x26000000))
+        ..rrect(color: const Color(0x0f000000))
+        ..rrect(color: const Color(0x0a000000))
+        ..rrect(color: const Color(0xffffffff)),
+    );
+
+    // Check what happens when disabled.
+    value = false;
+    await tester.pumpWidget(buildApp(enabled: false));
+    await tester.pumpAndSettle();
+
+    expect(focusNode.hasPrimaryFocus, isFalse);
+    expect(
+      find.byType(CupertinoSwitch),
+      paints
+        ..rrect(color: const Color(0x28787880))
+        ..clipRRect()
+        ..rrect(color: const Color(0x26000000))
+        ..rrect(color: const Color(0x0f000000))
+        ..rrect(color: const Color(0x0a000000))
+        ..rrect(color: const Color(0xffffffff)),
+    );
+  });
+
+  testWidgets('CupertinoSwitch.onFocusChange callback', (WidgetTester tester) async {
+    final FocusNode focusNode = FocusNode(debugLabel: 'CupertinoSwitch');
+    bool focused = false;
+    await tester.pumpWidget(
+      Directionality(
+      textDirection: TextDirection.ltr,
+      child: Center(
+        child: CupertinoSwitch(
+            value: true,
+            focusNode: focusNode,
+            onFocusChange: (bool value) {
+              focused = value;
+            },
+            onChanged:(bool newValue) {},
+          ),
+        ),
+      ),
+    );
+
+    focusNode.requestFocus();
+    await tester.pump();
+    expect(focused, isTrue);
+    expect(focusNode.hasFocus, isTrue);
+
+    focusNode.unfocus();
+    await tester.pump();
+    expect(focused, isFalse);
+    expect(focusNode.hasFocus, isFalse);
+  });
 }