bug(mat-chip-grid): impossible to navigate to the input using VoiceOver commands when there are chips selected

### 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 nesting input inside of the mat-chip-grid, it becomes inaccessible with the screenreader commands (when there are chips selected).

### Reproduction

StackBlitz link: https://stackblitz.com/run?file=src%2Fexample%2Fchips-input-example.html
Steps to reproduce:
1. Use material chips with input, where input is nested inside of mat-chip-grid.
2. Add at least one chip.
3. Start VoiceOver and focus the form field.
4. Navigate inside the form field using VoiceOver commands (e.g. VO-Right Arrow to move to the next item)

### Expected Behavior

It should be possible to focus the input element when pressing VO-Right Arrow inside the mat-chip-grid. Similar to how it is in chip-autocomplete example, when input is not inside the mat-chip-grid:
https://stackblitz.com/run?file=src%2Fexample%2Fchips-autocomplete-example.css

### Actual Behavior

Only chips and delete buttons can be focused using VoiceOver commands.

### Environment

- Angular: 19.0.5
- CDK/Material: 19.0.5
- Browser(s): Chrome
- Operating System (e.g. Windows, macOS, Ubuntu): MacOS

首先，在链接的 StackBlitz 示例中使用 macOS 和 VoiceOver 运行 Angular Material 19.0.5，添加一个 chip 后按照列出的步骤操作，以复现该问题。阅读 mat-chip-grid 和 chip-autocomplete 示例，比较焦点行为；当 VO-Right Arrow 可以到达嵌套的 input，同时 chips 仍保持选中状态时，即表示完成。

由索引模型根据 Issue 内容生成。