bug(form-field): Outlined form-field should have enough space to contain floating label

### Is this a regression?

- [ ] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

_No response_

### Description

When using `outline` appearance for `mat-form-field`, the floating label overflows out of component itself. The `mat-form-field` component should have enough space on top to contain floating label. See below screenshot for reference:

### Reproduction

StackBlitz link: https://stackblitz.com/edit/rxp9hmcc?file=src%2Fexample%2Fform-field-appearance-example.html

### Expected Behavior

The `mat-form-field` component should have enough space (margin) on top to contain floating label.

### Actual Behavior

The `mat-form-field` component does not have enough space (margin) on top to contain floating label.

### Environment

- Angular: 20
- CDK/Material: 20
- Browser(s): Chrome
- Operating System (e.g. Windows, macOS, Ubuntu): macOS

先从链接的 StackBlitz 复现和其中的表单字段外观示例开始，然后检查 Angular Material 中与浮动标签相关的 outlined mat-form-field 布局和样式。当 outlined 组件为浮动标签提供足够的顶部空间，且在报告的 Angular 20、Chrome 和 macOS 设置中不会发生溢出时，即视为完成。

由索引模型根据 Issue 内容生成。