Support cancellation for closing TabControl

[AZhrZho]

1. added a cancellation mechanism for closing TabItem. Resolves TabControl close button : provide a way to intercept "closeRequest" and be able to prevent closing #204
2. fixed a exception when closing TabItem while using ItemsSource.
3. added a project for testing.

[NotYoojun]

Great, I'll consider adding this feature example into the gallery btw.

[NotYoojun]

TL;DR: Approved &merged 🎉 thank you for your contribution!

Amazing work, and heartfelt thanks for your contribution! 💖

We’ve reviewed your pull request, everything looks great, and it’s now part of the project.
Your changes will be included in the next release - keep an eye on the release notes for the shout‑out you deserve.

If you have follow‑up improvements, fresh ideas, or related fixes, we’d be thrilled to see another PR from you.
Every contribution, big or small, helps us grow stronger as a community.

If anyone later spots something that needs attention in this change, please open a new issue instead of commenting here - that way we can track and resolve it properly.

Thank you for helping us build not just great software, but a space where people create with kindness, passion, and shared purpose! 🌱

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