minor #2456 [TwigComponent] Document about unwanted behavior with ExposeInTemplate and computed methods (Kocal)

This PR was merged into the 2.x branch.

Discussion
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[TwigComponent] Document about unwanted behavior with `ExposeInTemplate` and computed methods

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Issues        | Fix #... <!-- prefix each issue number with "Fix #", no need to create an issue if none exist, explain below instead -->
| License       | MIT

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As spotted when working on my application, the following code triggers two times the methods `transactions()` because of the presence of `#[ExposeInTemplate]` (because before I used `transactions` instead of `computed.transactions`):

```php
	#[ExposeInTemplate]
    public function transactions(): array
    {
        // SQL query to database
    }
```

```twig
{{ computed.transactions|length }}
```

When I remove `#[ExposeInTemplate]`, then only one SQL query is made.

Commits
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16cd48a [TwigComponent] Document about unwanted behavior with ExposeInTemplate and computed methods

Author: Kocal

src/TwigComponent/doc/index.rst

@@ -382,7 +382,7 @@ use the full path of the template where the macro is defined:
     <twig:Alert>
         {# ❌ this won't work #}
         {% from _self import message_formatter %}
-        
+
         {# ✅ this works as expected #}
         {% from 'path/of/this/template.html.twig' import message_formatter %}
 
@@ -1553,6 +1553,12 @@ are called additional times, the cached value is used.
     Computed methods only work for component methods with no required
     arguments.
 
+.. tip::
+
+    Ensure to not use the ``ExposeInTemplate`` attribute on a computed method,
+    otherwise the method will be called twice instead of only once, leading to
+    unnecessary overhead and potential performance issues.
+
 Events
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