bug(form-field): Label overlaps matPrefix in mat-tab-group on tab change

### 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 a mat-form-field with appearance="outline" and a matPrefix (e.g., an icon) is placed inside a mat-tab within a mat-tab-group, the mat-label (acting as a placeholder) overlaps with the matPrefix icon after switching tabs.

The issue is typically observed as follows:
- The form field renders correctly on the initially selected tab.
- When switching to a different tab containing a similar form field, the label of that form field incorrectly overlaps the prefix icon.
- Switching back to the first tab might then also show the overlap.

This behavior makes the form field difficult to read and use.


### Reproduction

StackBlitz link: [Link](https://stackblitz.com/edit/stackblitz-starters-sqfx3qcf?file=src%2Findex.html)

### Expected Behavior

The mat-label (placeholder) of the mat-form-field should always be positioned correctly to the right of the matPrefix icon, without any overlap, regardless of tab switching. The prefix icon should create sufficient space for itself, and the label should respect this space when not floated.

### Actual Behavior

After switching to a tab that was not initially active, the mat-label (placeholder) of the mat-form-field incorrectly overlaps with the matPrefix icon. The label does not seem to account for the space occupied by the prefix. This issue is consistently reproducible with the provided minimal reproduction steps.

### Environment

- Angular: 19.0.5
- CDK/Material: 19.0.4
- Browser(s): Google Chrome
- Operating System (e.g. Windows, macOS, Ubuntu):
Edition Windows Server 2025 Datacenter Evaluation
Version 24H2
OS build 26100.2894

提供された StackBlitz の再現手順から始め、mat-tab-group のタブを切り替えて、label と matPrefix が重なっていることを確認します。Angular Material のソースで mat-form-field と mat-tab-group の動作を追跡します。タブを切り替えた後も label が prefix の横に正しく配置されたままになれば完了です。

索引モデルが issue の本文から書いたものです。