core-data: Move setNestedValue to block editor package

[tyxla]

What?

This PR moves the setNestedValue utility function to the block editor package, alongside the rest of the object utils.

Why?

We need to utilize it to unblock #52404.

How?

We're just moving some code and making it a private API.

Testing Instructions

Verify all checks are green.

Testing Instructions for Keyboard

None

Screenshots or screencast

None

[Mamaduka]

Can we use a different package or even duplicate the helper method?

The block-editor shouldn't be a core-data dependency; the only reason it's there is because of the "Footnotes" feature, but that might change soon. See #51201 (comment).

cc @mcsf

[tyxla]

That makes sense. It felt odd that @wordpress/block-editor was a dependency of @wordpress/core-data, but since it was already the case I thought I'd exploit it.

I'm happy to duplicate it and then deduplicate it in another PR. Closing this one then.

[Mamaduka]

Thanks, @tyxla, and sorry for adding extra work.

[tyxla]

@Mamaduka no reason to be sorry! I actually truly appreciate how thorough and helpful your reviews have been 🙌