fix: DOMContentLoaded is not firing for inline module scripts

[istarkov]

Description

closes #3724

Steps for reproduction

https://embed.staging.webstudio.is/builder/f3843f61-c4dd-4fc6-9463-bb88e8cc5f9b

2 "Client Only" Embeds

<!--Embed 1 -->
<script type="module">
  import _ from 'https://cdn.jsdelivr.net/npm/lodash-es/lodash.js';

  console.log(_.join(['Hello', 'World', '1'], ' '));

  document.addEventListener('DOMContentLoaded', (event) => {
    console.log('DOM fully loaded 1');
  });
</script>

<!--Embed 2 -->
<script type="module">
  console.log('Hello 2');
  document.addEventListener('DOMContentLoaded', (event) => {
    console.log('DOM fully loaded 2');
  });
</script>

Before this PR gave output with following errors:

• Broken order
• Broken DOMContentLoaded

Hello 2
Hello World 1

Now no issues

Hello World 1
Hello 2
DOM fully loaded 1
DOM fully loaded 2

Code Review

• hi @kof, I need you to do
  • conceptual review (architecture, feature-correctness)
  • detailed review (read every line)
  • test it on preview

Before requesting a review

• made a self-review
• added inline comments where things may be not obvious (the "why", not "what")

Before merging

• tested locally and on preview environment (preview dev login: 5de6)
• updated test cases document
• added tests
• if any new env variables are added, added them to .env file