feat: built-in 'underline' for form control

### Prerequisites

- [X] I have read the [Contributing Guidelines](https://github.com/ionic-team/ionic-framework/blob/main/.github/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 include this feature request, without success.

### Describe the Feature Request

According to this issue : #27236

I am trying to achieve the original look and behavior with new modern syntax about label and AT.

https://stackblitz.com/edit/3we1ad-kzmne4?file=index.html

As you can see, the underline in original is resembling the underline in real paper form for user to fill in the blank.

(But what I tried to do result in the whole thing got underlined, including the label)

It would be nice to have built-in support functionality about this. for each form control (ion-input, ion-select, ion-textarea)

### Describe the Use Case

I am trying to achieve the original look and behavior with new modern syntax about label and AT.

https://stackblitz.com/edit/3we1ad-kzmne4?file=index.html

### Describe Preferred Solution

_No response_

### Describe Alternatives

_No response_

### Related Code

https://stackblitz.com/edit/3we1ad-kzmne4?file=index.html

### Additional Information

As I mentioned, it should be customizable, especially the length (where you want it to underline, the whole, or exclude label and just the fill in area).