bug: ion-item and ion-input UI inconsistency border line with helper and error text

还没有人认领这个 Issue。

### Prerequisites

- [X] I have read the [Contributing Guidelines](https://github.com/ionic-team/ionic-framework/blob/main/docs/CONTRIBUTING.md#creating-an-issue).
- [X] I agree to follow the [Code of Conduct](https://ionicframework.com/code-of-conduct).
- [X] I have searched for [existing issues](https://github.com/ionic-team/ionic-framework/issues) that already report this problem, without success.

### Ionic Framework Version

v7.x, v8.x

### Current Behavior

When using ion-input with helper or error text inside an ion-item, the ion-item renders its own border, and the ion-input renders a separate border around the helper or error text. This results in overlapping or duplicate borders, causing an inconsistent UI that looks cluttered and unappealing.

This behavior stems from a change in Ionic 7, where ion-input is decoupled from ion-item, and helper/error text must now be provided directly to ion-input. This design choice creates a challenge in maintaining the consistent structure expected when using ion-list, as all child components should typically be ion-item.

While a similar issue was reported for the counter feature in ion-input (see [Ionic Framework issue #27939](https://github.com/ionic-team/ionic-framework/issues/27939)), the resolution was to update the documentation and suggest avoiding the use of ion-item in cases where the counter is required. However, this workaround is not ideal for the current scenario. It undermines the consistent usage of ion-item as a child of ion-list and forces developers to conditionally remove or reintroduce ion-item depending on attributes like helper or error text. This breaks the cohesive design paradigm that Ionic promotes.

### Expected Behavior

The integration of ion-input and ion-item should allow for seamless styling, ensuring that only a single border is displayed when using helper or error text. This could be achieved by ensuring compatibility between ion-input and ion-item, or by providing clear documentation and design guidelines to maintain a consistent and visually appealing UI when both components are used together.

### Steps to Reproduce

1. Create an Ionic project using Ionic 7 or 8.
2. Add an ion-list and include multiple ion-item components.
3. Inside one of the ion-item components, add an ion-input with helper or error text.
4. Observe the overlapping borders or inconsistent styling between ion-item and the ion-input with helper/error text.

### Code Reproduction URL

https://stackblitz.com/edit/angular-2cisuedg?file=src%2Fapp%2Fexample.component.html

### Ionic Info

```
Ionic:

Ionic CLI : 7.2.0
Ionic Framework : @ionic/angular 7.6.6
@angular-devkit/build-angular : 18.2.12
@angular-devkit/schematics : 18.2.12
@angular/cli : 18.2.12
@ionic/angular-toolkit : 11.0.1

Capacitor:

Capacitor CLI : 6.2.0
@capacitor/android : 6.2.0
@capacitor/core : 6.2.0
@capacitor/ios : 6.2.0

Cordova:

Cordova CLI : not installed
Cordova Platforms : not available
Cordova Plugins : not available

Utility:

cordova-res : not installed globally
native-run : 2.0.1

System:

NodeJS : v20.10.0 (C:\Program Files\nodejs\node.exe)
npm : 10.2.3
OS : Windows 10
```

### Additional Information

_No response_

从链接的 StackBlitz 复现开始，检查带有辅助文本或错误文本的 ion-item 和 ion-input 组合。验证在报告的 Ionic 版本中是否存在重复或重叠的边框，然后确定该问题是通过组件样式兼容性解决，还是需要记录使用指导。完成的标准是 integration 呈现单一且一致的边框，或清晰记录受支持的结构。

由索引模型根据 Issue 内容生成。