Add ability to customize the default Slider padding (#156143)
Fixes [Ability to change Sliders padding](https://github.com/flutter/flutter/issues/40098)
Add ability to override default padding so the Slider can fit better in a layout.
### Code sample
<details>
<summary>expand to view the code sample</summary>
```dart
import 'package:flutter/material.dart';
void main() => runApp(const MyApp());
class MyApp extends StatefulWidget {
const MyApp({super.key});
@override
State<MyApp> createState() => _MyAppState();
}
class _MyAppState extends State<MyApp> {
double _sliderValue = 0.5;
@override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
theme: ThemeData(
sliderTheme: const SliderThemeData(
padding: EdgeInsets.symmetric(vertical: 4.0),
thumbColor: Colors.red,
inactiveTrackColor: Colors.amber,
),
),
home: Scaffold(
body: Directionality(
textDirection: TextDirection.ltr,
child: Center(
child: Card(
shape: const RoundedRectangleBorder(
borderRadius: BorderRadius.all(Radius.circular(4.0)),
),
color: Theme.of(context).colorScheme.surfaceContainerHighest,
margin: const EdgeInsets.symmetric(horizontal: 16.0),
child: Padding(
padding: const EdgeInsets.all(16.0),
child: Column(
mainAxisSize: MainAxisSize.min,
children: [
const Placeholder(fallbackHeight: 100.0),
Slider(
value: _sliderValue,
onChanged: (double value) {
setState(() {
_sliderValue = value;
});
},
),
const Placeholder(fallbackHeight: 100.0),
],
),
),
),
),
),
),
);
}
}
```
</details>
### Before
(Cannot adjust default `Slider` padding to fill the horizontal space in a `Column` and reduce the padded height)
<img width="717" alt="Screenshot 2024-10-03 at 15 45 18" src="https://github.com/user-attachments/assets/e9d9a4d1-3087-45b4-8607-b94411e2bd23">
### After
Can adjust default `Slider` padding via `SliderTheme`)
<img width="717" alt="Screenshot 2024-10-03 at 15 46 25" src="https://github.com/user-attachments/assets/cd455881-6d52-46cb-8ac6-cc33f50a13ff">
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