WeakEventListener has [EditorBrowsable(EditorBrowsableState.Never)] attribute

### Describe the bug

The WeakEventListener class is marked with the [EditorBrowsable(EditorBrowsableState.Never)] attribute. Is there a reason for this? The class seems to be quite useful for general use.

### Steps to reproduce

```text
Try to find WeakEventListener with IntelliSense
```

### Expected behavior

WeakEventListener can be found with IntelliSense

### Screenshots

_No response_

### Code Platform

- [ ] UWP
- [X] WinAppSDK / WinUI 3
- [ ] Web Assembly (WASM)
- [ ] Android
- [ ] iOS
- [ ] MacOS
- [ ] Linux / GTK

### Windows Build Number

- [ ] Windows 10 1809 (Build 17763)
- [ ] Windows 10 1903 (Build 18362)
- [ ] Windows 10 1909 (Build 18363)
- [ ] Windows 10 2004 (Build 19041)
- [ ] Windows 10 20H2 (Build 19042)
- [ ] Windows 10 21H1 (Build 19043)
- [ ] Windows 10 21H2 (Build 19044)
- [ ] Windows 10 22H2 (Build 19045)
- [X] Windows 11 21H2 (Build 22000)
- [ ] Other (specify)

### Other Windows Build number

_No response_

### App minimum and target SDK version

- [ ] Windows 10, version 1809 (Build 17763)
- [ ] Windows 10, version 1903 (Build 18362)
- [ ] Windows 10, version 1909 (Build 18363)
- [X] Windows 10, version 2004 (Build 19041)
- [ ] Windows 10, version 2104 (Build 20348)
- [ ] Windows 11, version 22H2 (Build 22000)
- [ ] Other (specify)

### Other SDK version

_No response_

### Visual Studio Version

2022

### Visual Studio Build Number

_No response_

### Device form factor

_No response_

### Additional context

_No response_

### Help us help you

Yes, I'd like to be assigned to work on this item.

Beginne damit, die Klasse WeakEventListener zu finden und ihr Attribut EditorBrowsable(EditorBrowsableState.Never) zu untersuchen. Prüfe, wie die Klasse im WinAppSDK/WinUI 3-Projekt verfügbar gemacht wird, und verifiziere nach der Bearbeitung des Attributs das IntelliSense-Verhalten; abgeschlossen ist die Aufgabe, wenn WeakEventListener über IntelliSense gefunden werden kann, ohne bestehende Tests oder Builds zu beeinträchtigen.

Vom Indexierungsmodell aus dem Issue-Text verfasst.