fix(overlays): fix an edge case in hiding outside elements

[alirezamirian]

When working with WYSIWYG editors or similar components that mutate the dom, the order or dome mutations could be in a way that dom mutation observer is called for elements that are not yet appended to the modal dom at the time MutationObserver callback is called.

This change adds a safe-guard for such cases, by checking if the target element is connected, as otherwise it will be considered outside the currently visible elements.

Closes #9364

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices

📝 Test Instructions:

🧢 Your Project:

[alirezamirian]

Adding a simple test case without using ReactQuill is a little tricky. let me know if you think it's a must to have it covered by a test case and I'll make another attempt.

[snowystinger]

I think it might be good to do a little more digging to make a test case if you don't mind.

I think you just need to append a child, then remove it, then trigger the mutation observer, then append it again and trigger the mutation observer again.

Might be worth investigating if Quill has a bug, because I'm not sure why it's doing this.