[Accessibility] Overlay DOM position breaks screen reader focus order for mat-menu

### 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

This bug was reported previously (https://github.com/angular/components/issues/10302
) and it seems that there was a fix made for autocomplete and select (https://github.com/angular/components/issues/10302#issuecomment-3574921653) but the issue still exists for menu.

### Reproduction

StackBlitz link:
https://stackblitz.com/angular/qyybdrnxmyx?file=main.ts

Steps to reproduce:
1. Click "Menu". The screen reader focus is moved to Item 1.
2. Navigate back (ctrl+option+left). This moves to the menu itself (no problem there).
3. Navigate back again. This moves focus to "Current build: ...." instead of the original Menu button. On a larger page, this problem will be made worse by all the other elements in between.

### Expected Behavior

A focus-trap should be applied to the overlay, and the rest of the page should be inaccessible while the overlay is displayed, with or without a screen reader.

### Actual Behavior

If you shift focus backwards in a screen reader when a component like MatMenu creates an overlay, it brings you to the bottom of the page instead of to the flyout origin.

### Environment

- Angular: 19.2.10
- CDK/Material: 19.2.19
- Browser(s): Google Chrome Version 145.0.7632.117 (
- Operating System (e.g. Windows, macOS, Ubuntu): macOS Sequoia 15.6

Beginne mit der verknüpften StackBlitz-Reproduktion und ihrem main.ts-Einstiegspunkt. Verfolge anschließend das mat-menu-Overlay und das Fokusverhalten im Quellcode der Angular-Komponenten. Bestätige die Reproduktion mit einem Screenreader und verwende den erwarteten Rückwärtsnavigationspfad als Abschlusskriterium: Der Fokus kehrt zum ursprünglichen Menu button zurück, und der Hintergrund ist unzugänglich, solange das Menü geöffnet ist.

Vom Indexierungsmodell aus dem Issue-Text verfasst.