bug(datepicker): Focus Not Properly Managed After Selecting Date in Angular Datepicker (VoiceOver, iOS)

### 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

The Angular date picker doesn't properly focus on the selected date when using VoiceOver on iOS. When I try to select a date, the calendar opens as expected, and I double-tap to choose a date using VoiceOver. However, after the date is selected, the double-tap also triggers a selection on whatever element is behind the calendar.

### Reproduction

Steps to reproduce:
1. Enable VoiceOver on iOS.
2. Navigate to [Angular Material Datepicker](https://material.angular.dev/components/datepicker/overview).
3. Open the datepicker; the calendar overlay appears.
4. Using VoiceOver, double-tap to select a date.
5. After the double-tap, focus unexpectedly shifts to an element behind the calendar instead of remaining within the datepicker.


### Expected Behavior

After selecting a date using VoiceOver, the focus should return to the datepicker input, not shift to elements behind the calendar.

### Actual Behavior

After selecting a date with VoiceOver, the focus shifts to an element behind the calendar instead of returning to the datepicker input.

### Environment

- Angular: 18, 20
- CDK/Material: 18, 20
- Browser(s): Safari, Chrome, Brave
- Operating System (e.g. Windows, macOS, Ubuntu): iOS

まず、記載されている手順を使用して、iOS 上で VoiceOver を有効にし、Angular Material Datepicker の概要にある問題を再現します。日付選択後の datepicker のフォーカス処理を調査し、カレンダーの背後にある要素ではなく datepicker の入力にフォーカスが戻ることを確認します。既存の datepicker テストでこの問題を確認できる場合は、回帰テストでこの動作をカバーします。

索引モデルが issue の本文から書いたものです。