Add test for animated_size.0.dart API example.

[ksokolovskyi]

This PR contributes to #130459

Description

• Updates examples/api/lib/widgets/animated_size/animated_size.0.dart API example by using SizedBox to size the surrounding of the FlutterLogo while setting the constant FlutterLogo size. This was done because FlutterLogo already has size animation under the hood, and the main goal of this example is to show AnimatedSize usage
• Adds test for examples/api/lib/widgets/animated_size/animated_size.0.dart

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I signed the [CLA].
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is [test-exempt].
• I followed the [breaking change policy] and added [Data Driven Fixes] where supported.
• All existing and new tests are passing.

[bleroux]

Great test!
One minor comment related to formatting and one question.

[bleroux]

Nice simplification!

[bleroux]

Any reason to not animate the FlutterLogo the way it was done before? I think the visual effect made sense and the sample will be a little easier to understand when removing the SizedBox.

[ksokolovskyi]

@bleroux
This was done because FlutterLogo already has size animation under the hood, and the main goal of the example is to show AnimatedSize usage. You can try the following code sample to verify that FlutterLogo animates without the usage of AnimatedSize.

Code sample

// 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';

/// Flutter code sample for [AnimatedSize].

void main() => runApp(const AnimatedSizeExampleApp());

class AnimatedSizeExampleApp extends StatelessWidget {
  const AnimatedSizeExampleApp({super.key});

  static const Duration duration = Duration(seconds: 1);
  static const Curve curve = Curves.easeIn;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text('AnimatedSize Sample')),
        body: const Center(
          child: AnimatedSizeExample(
            duration: duration,
            curve: curve,
          ),
        ),
      ),
    );
  }
}

class AnimatedSizeExample extends StatefulWidget {
  const AnimatedSizeExample({
    required this.duration,
    required this.curve,
    super.key,
  });

  final Duration duration;

  final Curve curve;

  @override
  State<AnimatedSizeExample> createState() => _AnimatedSizeExampleState();
}

class _AnimatedSizeExampleState extends State<AnimatedSizeExample> {
  bool _isSelected = false;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: () {
        setState(() {
          _isSelected = !_isSelected;
        });
      },
      child: Center(
        child: ColoredBox(
          color: Colors.amberAccent,
          child: FlutterLogo(
            size: _isSelected ? 250.0 : 100.0,
          ),
        ),
      ),
    );
  }
}

[bleroux]

LGTM!

[TahaTesser]

LGTM!

[ksokolovskyi]

@bleroux @TahaTesser thanks for the review!