What?

Fixes a bug that happens with nested data-wp-each elements that use the same key for the items they render. E.g., in the following HTML, there are two different lists that use the same item key:

<ul 
	data-wp-interactive="directive-each"
	data-testid="nested-with-same-item-key"
>
	<template data-wp-each="context.list" data-wp-context='{"list":["parent1","parent2"]}'>
		<template data-wp-each="context.list" data-wp-context='{"list":["child1","child2"]}'>
			<li data-wp-text="context.item"></li>
		</template>
		<li data-wp-text="context.item"></li>
	</template>
</ul>

The resulting HTML, once the directives are evaluated in the client, is this:

<ul 
	data-wp-interactive="directive-each"
	data-testid="nested-with-same-item-key"
>
	<li data-wp-text="context.item">child2</li>
	<li data-wp-text="context.item">child2</li>
	<li data-wp-text="context.item">child2</li>
	<li data-wp-text="context.item">child2</li>
	<li data-wp-text="context.item">child2</li>
	<li data-wp-text="context.item">child2</li>
</ul>

This happens because, instead of shadowing the inherited item prop from the parent, the child contexts are modifying the inherited item prop. In short, all children modify the same prop sequentially and inherit the same value.

With the changes included in this PR, the final result is as expected.

<ul 
	data-wp-interactive="directive-each"
	data-testid="nested-with-same-item-key"
>
	<li data-wp-text="context.item">child1</li>
	<li data-wp-text="context.item">child2</li>
	<li data-wp-text="context.item">parent1</li>
	<li data-wp-text="context.item">child1</li>
	<li data-wp-text="context.item">child2</li>
	<li data-wp-text="context.item">parent2</li>
</ul>

Why?

This case should be supported. The server-side directive processing already generates the proper HTML.

How?

Instead of changing the property in the context with key [itemProp] after defining the local context, which actually points to the inherited property of the parent context, the local context is instantiated with the [itemProp] property, effectively shadowing the parent one.

Testing Instructions

1. In a page with interactive blocks, add a Custom HTML block with the code above.
2. Visit that page.
3. Ensure the HTML is the expected one.