fix: clone and copy styles

[kptdobe]

Fix #183

2 options to fix the issue:

• revert the document.cloneNode(true) and use the original. This would require the enduser to click on import each time they want to get a fresh document to work on
• copy the styles we need - since document.cloneNode(true) does not copy the style, we need to inline them in the clone

With this PR, we need to traverse the document to copy and inline the style properties defined as required. By default, only background-image is defined. But the list could be controlled in import.js via:

export default {
  transformDOM() {...},
  REQUIRED_STYLES: ['background-image', /* add more here if needed */],

[catalan-adobe]

LGTM! Though I think it deserves an entry in the import guidelines to explain how to add style properties to clone.

[catalan-adobe]

LGTM! Tested on a bacom url + importer, issue fixed. And thanks for the documentation :)

[github-actions]

🎉 This PR is included in version 1.39.1 🎉

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