Preserve styled markup in Code

Fixes #205

As it stands right Current Code block I'm testing with:

<!-- wp:code {"highlightedLines":"4-18","showLineNumbers":true} -->
<pre class="wp-block-code"><code>&lt;br&gt;
&amp;amp;
&lt;script&gt;
if ( true &amp;&amp; "foo" &lt;= 'bar' &amp;&amp; 'baz' &gt;= "quux" ) 
{} else if ( 
  "<strong>bolded</strong>" &amp;&amp; 
  "<em>italicized</em>" &amp;&amp; 
  "<a href="https://example.com/">linked</a>" &amp;&amp; 
  "<strong><em><a href="https://example.com">all</a></em></strong>" ) 
{} else if ( 
  "bolded spanning <strong>tokens" == 123</strong> 
) {} else if ( 
  "italicized spanning <em>tokens" == null</em> 
) {} else if ( 
  "link spanning <a href="https://example.com">tokens" == true</a> 
) {} else {
  // &#91;gallery]
}
&lt;/script&gt;
&#91;test]
&#91;embed]https://twitter.com/WordPress/status/1631756836666785795&#91;/embed]

https:&#47;&#47;twitter.com/WordPress/status/1631756836666785795

&#91;sic]</code></pre>
<!-- /wp:code -->

It's currently rendered as:

Without plugin	Editor	Frontend

Notice that the shortcodes are no longer being rendered, which is a fix. But what is still broken is the handling of stylized text inside the Code block. It is is getting corrupted by highlight.php.

This PR seeks to address this by adding the formatting back in after the code has been highlighted.

westonruter / syntax-highlighting-code-block

Preserve styled markup in Code #698