bug(overlay): Weird tooltip issue with the new popover overlay.

### Is this a regression?

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

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

v20

### Description

We detected a weird issue with tooltips regarding the popover introduced in v21.
When I put a tooltip on a mat-select, hover over the mat-select, the tooltip is shown. Then I open the mat select and move out my mouse from the browser and bring the mouse back to the browser, the tooltip is shown no matter where i am hovering on with my mouse.
Usually, it is solved after the mat select is closed and opened, then i cannot repro anymore.
But reloading the page and doing it the first time is usually a good repro for the issue.

I'm not sure if I could explain the repro correctly, so here is a short gif:

I scrolled through issues that can be related to my issue, and found this one: https://github.com/angular/components/issues/32642
Turning off the new popover with
`{ provide: OVERLAY_DEFAULT_CONFIG, useValue: { usePopover: false } },` solves the issue.
I cannot reproduce it anymore with usePopover: false.

### Reproduction

StackBlitz link: https://stackblitz.com/edit/stackblitz-starters-3qpcms44?file=package.json,src%2Fmain.ts
Steps to reproduce:
1. Open the page the first time
2. Hover over the mat select
3. Open the mat select
4. Move the mouse outside of the browser
5. Bring back the mouse
6. The tooltip will be shown no matter where i hover over on the page

### Expected Behavior

The tooltip should not be shown everywhere.

### Actual Behavior

The tooltip is shown everywhere.

### Environment

- Angular: v21.1.2
- CDK/Material: v21.1.2
- Browser(s): Chrome latest
- Operating System (e.g. Windows, macOS, Ubuntu): Windows

从链接的 StackBlitz reproduction 开始，重点查看 package.json 和 src/main.ts，并在启用 usePopover 的情况下按照 tooltip/mat-select 步骤操作。在 Chrome 中确认首次加载时的行为；完成的标准是离开浏览器并重新进入后，tooltip 不再显示在整个页面上，同时普通 tooltip 仍会显示在 mat-select 上。

由索引模型根据 Issue 内容生成。