Core Data: Allow useEntityProp setter to accept an updater function

[Adi-ty]

What?

This PR implements updater function support for the useEntityProp hook, addressing the stale closure issue.

Closes #70748

Why?

When using useEntityProp in async functions, stale closures can lead to data loss. The existing setter requires a static value, which can become outdated during async operations.

How?

Updated Hook Logic: Modified the setValue function to accept updater functions. If newValue is a function, it will receive the current state. This prevents stale data issues by ensuring the setter captures the most recent state when invoked.

Testing Instructions

1. Create a test component that uses useEntityProp:

   const [meta, setMeta] = useEntityProp('postType', 'post', 'meta', postId);

2. Test backward compatibility - verify static values still work:

   setMeta({ key: 'static value' }); 

3. Test new updater function - verify the new functionality:

   setMeta((currentMeta) => ({ ...currentMeta, newKey: 'value' }));

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Co-authored-by: Adi-ty <iamadisingh@git.wordpress.org>
Co-authored-by: cr0ybot <cr0ybot@git.wordpress.org>
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[cr0ybot]

This is perhaps a little vague for someone that doesn't know what an updater function usually looks like. A "Usage" section like useEntityRecord has would be really nice.

I would suggest something like the following:

import { useEntityProp } from '@wordpress/core-data';

function MetaUpdater( { postType, postId } ) {
	const [ meta, setMeta ] = useEntityProp( 'postType', postType, 'meta', postId );

	const handleSyncUpdate = () => {
		const result = syncTask();

		// Use setter with a static value:
		setMeta( { ...meta, taskKey: result } );
	};

	const handleAsyncUpdate = async () => {
		const result = await asyncTask();

		// Use setter with an updater function:
		setMeta( ( currentMeta ) => { ...currentMeta, taskKey: result } );
	};
}

[Adi-ty]

@cr0ybot Thank you for the feedback! I've added your suggested usage section.