Core Data: Add util for minimally modifying items.

[epiqueras]

Extracted from #16761

Description

This PR adds a utility for minimally modifying items, to the core data package in preparation for refactoring the editor store to rely entirely on core/data entities. The utility maps an item to a new item, retaining non primitive value references where possible (where deeply equal). This is necessary so that components that depend on these values don't update unnecessarily.

How has this been tested?

Unit tests were written and ran to test for expected functionality.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.

[youknowriad]

The utility looks good to me. I was wondering if we should use it in the RECEIVE_ITEMS action right now (without the full edit PR)

[epiqueras]

The utility looks good to me. I was wondering if we should use it in the RECEIVE_ITEMS action right now (without the full edit PR)

I opted not to, because then we would be doing what the editor store already does and hamper performance unnecessarily.