feat: Add hint (Widget) property to InputDecoration - #161424

…r/flutter#161424)

…r/flutter#161424)

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Adds a new property to InputDecoration `hintTextWidget`

*Fixes*: flutter#161130

With the introduction of ~hintTextWidget~ hint We should be able to
animate hintText



https://github.com/user-attachments/assets/7955a835-5f60-4451-8ede-b5e5f0457046


https://github.com/user-attachments/assets/55d7f021-cc8f-471e-a1d8-e601262ff640


<details>
<summary>sample code</summary>

```dart
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 MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);
  final String title;
  @OverRide
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
  String _searchText = 'Popular Picks';
  List<String> wordsToShow = [
    'Popular Picks',
    'Trending',
    'New Arrivals',
    'Best Sellers',
    'Top Rated',
  ];

  int index = 0;
  @OverRide
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Padding(
          padding: const EdgeInsets.all(8.0),
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              TextField(
                cursorHeight: 16,
                decoration: InputDecoration(
                  maintainHintHeight: true,
                  hintTextWidget: Row(
                    children: [
                      const Text(
                        "Search for ",
                        style: TextStyle(fontSize: 16),
                      ),
                      SlidingText(
                          onCompleted: () {
                            index = (index + 1) % wordsToShow.length;
                            setState(() {
                              _searchText = wordsToShow[index];
                            });
                          },
                          word: _searchText,
                          interval: 1500,
                          isDelay: true),
                    ],
                  ),
                  border: OutlineInputBorder(),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

class SlidingText extends StatefulWidget {
  final String word;
  final int interval;
  final bool isDelay;
  final Function onCompleted;

  const SlidingText({
    required this.word,
    required this.interval,
    required this.isDelay,
    required this.onCompleted,
    Key? key,
  }) : super(key: key);

  @OverRide
  _SlidingTextState createState() => _SlidingTextState();
}

class _SlidingTextState extends State<SlidingText>
    with SingleTickerProviderStateMixin {
  late AnimationController _animController;
  late Animation<Offset> _slideAnimation;
  late Animation<double> _fadeAnimation;

  @OverRide
  void initState() {
    super.initState();

    _animController = AnimationController(
      duration: Duration(milliseconds: widget.interval),
      vsync: this,
    );

    _slideAnimation = Tween<Offset>(
      begin: Offset(0, 0.5),
      end: Offset(0, -0.6),
    ).animate(
      CurvedAnimation(
        parent: _animController,
        curve: Curves.easeInOut,
      ),
    );
    _fadeAnimation = TweenSequence([
      TweenSequenceItem(
        tween: Tween<double>(begin: 0.0, end: 1.0).chain(
          CurveTween(curve: Curves.easeIn),
        ),
        weight: 50, // First half of the animation
      ),
      TweenSequenceItem(
        tween: Tween<double>(begin: 1.0, end: 0.0).chain(
          CurveTween(curve: Curves.easeOut),
        ),
        weight: 50, // Second half of the animation
      ),
    ]).animate(_animController);
    // add interval

    _animController.addStatusListener((status) async {
      if (status == AnimationStatus.completed) {
        await Future.delayed(Duration(milliseconds: 500));
        widget.onCompleted();
      }
    });
    _animController.forward();
  }

  @OverRide
  void didUpdateWidget(covariant SlidingText oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (oldWidget.word != widget.word) {
      _animController.reset();
      _animController.forward();
    }
  }

  @OverRide
  void dispose() {
    _animController.dispose();
    super.dispose();
  }

  @OverRide
  Widget build(BuildContext context) {
    return AnimatedBuilder(
      animation: _animController,
      builder: (context, child) {
        return SlideTransition(
          position: _slideAnimation,
          child: FadeTransition(
            opacity: _fadeAnimation,
            child: Text(
              widget.word,
              style: const TextStyle(fontSize: 16),
            ),
          ),
        );
      },
    );
  }
}

```
</details> 

## Pre-launch Checklist

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

If you need help, consider asking for advice on the #hackers-new channel
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…r/flutter#161424)