Improve callout shortcode. (#31802)

Remove the `markdownify` call, and instead rely on Hugo's proper syntax; `{{% callout %}}` when we want to the content to be processed as Markdown.

This allows for stuff like:

{{% callout info %}}
##### I'm an info callout!

```css
.foo {
  color: #fff;
}
```

{{< example >}}
<div class="alert alert-warning alert-dismissible fade show" role="alert">
  <strong>Holy guacamole!</strong> You should check in on some of those fields below.
  <button type="button" class="btn-close" data-dismiss="alert" aria-label="Close"></button>
</div>
{{< /example >}}
{{% /callout %}}

site/content/docs/5.0/components/carousel.md

@@ -12,9 +12,9 @@ The carousel is a slideshow for cycling through a series of content, built with
 
 In browsers where the [Page Visibility API](https://www.w3.org/TR/page-visibility/) is supported, the carousel will avoid sliding when the webpage is not visible to the user (such as when the browser tab is inactive, the browser window is minimized, etc.).
 
-{{< callout info >}}
+{{% callout info %}}
 {{< partial "callout-info-prefersreducedmotion.md" >}}
-{{< /callout >}}
+{{% /callout %}}
 
 Please be aware that nested carousels are not supported, and carousels are generally not compliant with accessibility standards.
 
@@ -324,9 +324,9 @@ Options can be passed via data attributes or JavaScript. For data attributes, ap
 
 ### Methods
 
-{{< callout danger >}}
+{{% callout danger %}}
 {{< partial "callout-danger-async-methods.md" >}}
-{{< /callout >}}
+{{% /callout %}}
 
 You can create a carousel instance with the carousel constructor, for example, to initialize with additional options and start cycling through items: