Repository: flutter
Issue: TextField.scrollPadding does not affect scrollable and scrollable decorations
Labels: a: text input,framework,f: material design,f: scrolling,has reproducible steps,P2,team-design,triaged-design,found in release: 3.13,found in release: 3.14

### Is there an existing issue for this?

- [X] I have searched the [existing issues](https://github.com/flutter/flutter/issues)
- [X] I have read the [guide to filing a bug](https://flutter.dev/docs/resources/bug-reports)

### Steps to reproduce

To reproduce 
1. Copy the code from the sample and run it
2. Type multiple letters till the scrollbar shows up
3. Scroll up and down to see the scrollbar out of the bounds of the textfield

The scrollbar is clipping out of the bounds of the textfield when the border is curved and to resolve this, scrollbar padding should work but it doesn't. 

P.s [Proposal] Providing an option to position the scrollbar in the center would also be a great add. (Not related to issue, Just asking from a unique design pov)

### Expected results

Two options
1. Even if the the scroll padding doesn't work, the scrollbar should be within the bounds of the textfield (like putting them in a row within a container) rather than stacking it above it.
4. Scroll padding should work,

### Actual results

Two results
1. Scrollbar isn't within the bounds of the textfield hence the clipping on the top right you'll see in the image provided.
2. `ScrollPadding` property of the textfield doesn't work at all (or maybe it serves another purpose and if so provide a way to add padding to the scrollbar)

### Code sample

<details><summary>Code sample</summary>

```dart
import 'package:flutter/material.dart';

void main() {
  runApp(const MainApp());
}

class MainApp extends StatelessWidget {
  const MainApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: const Home(),
      theme: ThemeData.light(useMaterial3: true),
    );
  }
}

class Home extends StatefulWidget {
  const Home({
    super.key,
  });

  @override
  State<Home> createState() => _HomeState();
}

class _HomeState extends State<Home> {
  late ScrollController scrollController;

  @override
  void initState() {
    super.initState();
    scrollController = ScrollController();
  }

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: Scaffold(
        body: Padding(
          padding: const EdgeInsets.all(30.0),
          child: Center(
            child: Scrollbar(
              controller: scrollController,
              thumbVisibility: true,
              child: TextField(
                scrollController: scrollController,
                keyboardType: TextInputType.multiline,
                minLines: 1,
                maxLines: 3,
                scrollPadding: const EdgeInsets.only(
                  right: 200,
                ), // Higher value to see if its working
                decoration: const InputDecoration(
                  hintText: 'Send a message ...',
                  hintStyle: TextStyle(fontSize: 14),
                  contentPadding: EdgeInsets.fromLTRB(24, 20, 12, 18),
                  alignLabelWithHint: true,
                  border: OutlineInputBorder(
                    borderRadius: BorderRadius.all(
                      Radius.circular(30),
                    ),
                  ),
                ),
              ),
            ),
          ),
        ),
      ),
    );
  }
}

```

</details>


### Screenshots or Video

<details>
<summary>Screenshots / Video demonstration</summary>

![demo](https://github.com/flutter/flutter/assets/107868140/6990e0f3-da48-4e39-beba-6a3614bfe024)


</details>


### Logs

_No response_

### Flutter Doctor output

<details><summary>Doctor output</summary>

```console
[√] Flutter (Channel stable, 3.10.6, on Microsoft Windows [Version 10.0.22621.2134],  
    locale en-US)
[√] Windows Version (Installed version of Windows is version 10 or higher)
[√] Android toolchain - develop for Android devices (Android SDK version 33.0.0)
[√] Chrome - develop for the web
[√] Visual Studio - develop for Windows (Visual Studio Community 2022 17.5.1)
[!] Android Studio (version 2021.2)
    X Unable to determine bundled Java version.
[√] Android Studio (version 2022.3)
[√] VS Code (version 1.81.1)
[√] Connected device (4 available)
[√] Network resources

! Doctor found issues in 1 category.
```

</details>