minor symfony#2699 key is more reliable with child components (weaverryan)

This PR was merged into the 2.x branch.

Discussion
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key is more reliable with child components

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Docs?         | yes
| Issues        | Fix symfony#1643
| License       | MIT

I couldn't track down why, but for child components, `key` is more reliable. When `id` is used and a child requires re-rendering (because input props changed), the dummy element returned by https://github.com/symfony/ux/blob/2.x/src/LiveComponent/src/EventListener/InterceptChildComponentRenderSubscriber.php will not have an `id`, but with `key` it will. Smells like a bug, but `key` works

Commits
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304acf8 key is more reliable with child components

Author: Kocal

src/LiveComponent/doc/index.rst

@@ -3202,14 +3202,14 @@ Rendering Quirks with List of Elements
 
 If you're rendering a list of elements in your component, to help LiveComponents
 understand which element is which between re-renders (i.e. if something re-orders
-or removes some of those elements), you can add a ``id`` attribute to
+or removes some of those elements), you can add a ``key`` attribute to
 each element
 
 .. code-block:: html+twig
 
     {# templates/components/Invoice.html.twig #}
     {% for lineItem in lineItems %}
-        <div id="{{ lineItem.id }}">
+        <div key="{{ lineItem.id }}">
             {{ lineItem.name }}
         </div>
     {% endfor %}
@@ -3224,10 +3224,6 @@ the list changes as the user types into a search box... or by clicking
 "delete" on an item. In this case, the wrong children may be removed
 or existing child components may not disappear when they should.
 
-.. versionadded:: 2.8
-
-    The ``key`` prop was added in Symfony UX Live Component 2.8.
-
 To fix this, add a ``key`` prop to each child component that's unique
 to that component:
 
@@ -3242,9 +3238,7 @@ to that component:
     {% endfor %}
 
 The ``key`` will be used to generate an ``id`` attribute,
-which will be used to identify each child component. You can
-also pass in a ``id`` attribute directly, but ``key`` is
-a bit more convenient.
+which will be used to identify each child component.
 
 .. _rendering-loop-new-element: