Update .sr-only mixin and utility (#25197)

* Remove clip-path from .sr-only utility as it causes perf regressions in Chrome

* change snippet to example

docs/4.0/utilities/screenreaders.md

@@ -12,9 +12,9 @@ Hide an element to all devices **except screen readers** with `.sr-only`. Combin
 Necessary for following [accessibility best practices]({{ site.baseurl }}/docs/{{ site.docs_version }}/getting-started/#accessibility).
 {%- endcomment -%}
 
-{% highlight html %}
+{% example html %}
 <a class="sr-only sr-only-focusable" href="#content">Skip to main content</a>
-{% endhighlight %}
+{% endexample %}
 
 {% highlight scss %}
 // Usage as a mixin