[doc] Update `suffixIcon`/`prefixIcon` for alignment with code snippet (#91998)

examples/api/lib/material/input_decorator/input_decoration.prefix_icon.0.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flutter code sample for InputDecorator
+
+import 'package:flutter/material.dart';
+
+void main() => runApp(const MyApp());
+
+class MyApp extends StatelessWidget {
+  const MyApp({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return const MaterialApp(
+      title: 'Input Decorator Sample',
+      home: Scaffold(body: InputDecoratorExample()),
+    );
+  }
+}
+
+class InputDecoratorExample extends StatelessWidget {
+  const InputDecoratorExample({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return const TextField(
+      decoration: InputDecoration(
+        border: OutlineInputBorder(),
+        labelText: 'Enter name',
+        prefixIcon: Align(
+          widthFactor: 1.0,
+          heightFactor: 1.0,
+          child: Icon(
+            Icons.person,
+          ),
+        ),
+      ),
+    );
+  }
+}

examples/api/lib/material/input_decorator/input_decoration.suffix_icon.0.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flutter code sample for InputDecorator
+
+import 'package:flutter/material.dart';
+
+void main() => runApp(const MyApp());
+
+class MyApp extends StatelessWidget {
+  const MyApp({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return const MaterialApp(
+      title: 'Input Decorator Sample',
+      home: Scaffold(body: InputDecoratorExample()),
+    );
+  }
+}
+
+class InputDecoratorExample extends StatelessWidget {
+  const InputDecoratorExample({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return const TextField(
+      decoration: InputDecoration(
+        border: OutlineInputBorder(),
+        labelText: 'Enter password',
+        suffixIcon: Align(
+          widthFactor: 1.0,
+          heightFactor: 1.0,
+          child: Icon(
+            Icons.remove_red_eye,
+          ),
+        ),
+      ),
+    );
+  }
+}

examples/api/test/material/input_decorator/input_decoration.prefix_icon.0_test.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_api_samples/material/input_decorator/input_decoration.prefix_icon.0.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('InputDecorator prefixIcon alignment', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.MyApp(),
+    );
+    expect(tester.getCenter(find.byIcon(Icons.person)).dy, 28.0);
+  });
+}

examples/api/test/material/input_decorator/input_decoration.suffix_icon.0_test.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_api_samples/material/input_decorator/input_decoration.suffix_icon.0.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('InputDecorator suffixIcon alignment', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.MyApp(),
+    );
+    expect(tester.getCenter(find.byIcon(Icons.remove_red_eye)).dy, 28.0);
+  });
+}

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

@@ -2945,12 +2945,24 @@ class InputDecoration {
   /// [icon] and above the widgets that contain [helperText],
   /// [errorText], and [counterText].
   ///
+  /// The prefix icon aligment can be changed using [Align] with a fixed `widthFactor` and
+  /// `heightFactor`.
+  ///
+  /// {@tool dartpad}
+  /// This example shows how the prefix icon alignment can be changed using [Align] with
+  /// a fixed `widthFactor` and `heightFactor`.
+  ///
+  /// ** See code in examples/api/lib/material/input_decorator/input_decoration.prefix_icon.0.dart **
+  /// {@end-tool}
+  ///
   /// See also:
   ///
   ///  * [Icon] and [ImageIcon], which are typically used to show icons.
   ///  * [prefix] and [prefixText], which are other ways to show content
   ///    before the text field (but after the icon).
   ///  * [suffixIcon], which is the same but on the trailing edge.
+  ///  * [Align] A widget that aligns its child within itself and optionally
+  ///    sizes itself based on the child's size.
   final Widget? prefixIcon;
 
   /// The constraints for the prefix icon.
@@ -3055,12 +3067,24 @@ class InputDecoration {
   /// [icon] and above the widgets that contain [helperText],
   /// [errorText], and [counterText].
   ///
+  /// The suffix icon aligment can be changed using [Align] with a fixed `widthFactor` and
+  /// `heightFactor`.
+  ///
+  /// {@tool dartpad}
+  /// This example shows how the suffix icon alignment can be changed using [Align] with
+  /// a fixed `widthFactor` and `heightFactor`.
+  ///
+  /// ** See code in examples/api/lib/material/input_decorator/input_decoration.suffix_icon.0.dart **
+  /// {@end-tool}
+  ///
   /// See also:
   ///
   ///  * [Icon] and [ImageIcon], which are typically used to show icons.
   ///  * [suffix] and [suffixText], which are other ways to show content
   ///    after the text field (but before the icon).
   ///  * [prefixIcon], which is the same but on the leading edge.
+  ///  * [Align] A widget that aligns its child within itself and optionally
+  ///    sizes itself based on the child's size.
   final Widget? suffixIcon;
 
   /// Optional widget to place on the line after the input.