Interactivity API: Update iterable signals when deepMerge() adds new properties

[DAreRodz]

What?

Fixes deepMerge() to update the corresponding internal signals for property iteration (i.e., ...obj, Object.keys( obj ), Reflect.ownKeys( obj ), etc.

Why?

When a deepMerge() call adds new properties to an object, the corresponding iterable signal should be updated to ensure subscribed directives react to changes.

How?

Modifying the corresponding signal for the target object when necessary.

Testing Instructions

A unit test was added that didn't pass before the bug fix.

[github-actions]

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Co-authored-by: DAreRodz <darerodz@git.wordpress.org>
Co-authored-by: michalczaplinski <czapla@git.wordpress.org>
Co-authored-by: cbravobernal <cbravobernal@git.wordpress.org>

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[github-actions]

Flaky tests detected in 7b7e0cf.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/10753358050
📝 Reported issues:

• [Flaky Test] Redirection after template creation #60678 in /test/e2e/specs/site-editor/site-editor-url-navigation.spec.js

[michalczaplinski]

Looks good to me! The change makes sense and has a passing test 👍

[cbravobernal]

Maybe "hasNewData" or "hasNewProperties" defines better the issue.

[DAreRodz]

Here, isNew refers to the current key inside the loop. But that's a good point anyway; we could move the signal update outside the loop. 🤔

[DAreRodz]

Done in d516c42.