[ObservableObject] Refactor ObservableObject docs a bit?

[citelao]

Today, the Observable Object docs make no mention of INotifyPropertyChangedAttribute or ObservableProperty. I began this draft to remedy this gap, only to realize that the API documentation is also fairly out of date.

Happy to help revise.

[learn-build-service-prod]

PoliCheck Scan Report

The following report lists PoliCheck issues in PR files. Before you merge the PR, you must fix all severity-1 and severity-2 issues. The AI Review Details column lists suggestions for either removing or replacing the terms. If you find a false positive result, mention it in a PR comment and include this text: #policheck-false-positive. This feedback helps reduce false positives in future scans.

✅ No issues found

More information about PoliCheck

Information: PoliCheck | Severity Guidance | Term
For any questions: Try searching the learn.microsoft.com contributor guides or post your question in the Learn support channel.

[learn-build-service-prod]

Learn Build status updates of commit e4e8638:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/mvvm/ObservableObject.md	✅Succeeded	View

For more details, please refer to the build report.

[citelao]

@microsoft-github-policy-service agree company="Microsoft"

I wrote this while working at Microsoft