Fix text missing after HTML tags

[compulim]

Fixes #5319.

Changelog Entry

Fixed

• Fixes #5319. Some Markdown text are not rendered after HTML tags, in PR #5320, by @compulim

Description

Our HTML parsing and serialization logic only handle .children but not .childNodes. Thus, it is omitting text nodes.

When dealing with certain types of Markdown, the text may not be wrapped in <p>. For example,

Line 1

<br />
Line 2

Will be converted to HTML and "Line 2" is not wrapped in <p> and is a text node.

<p>Line 1</p><br />Line 2

Specific Changes

• Updates serializeDocumentIntoString and useRenderMarkdownAsHTML to handle text nodes

• I have added tests and executed them locally
• I have updated CHANGELOG.md
• I have updated documentation

Review Checklist

This section is for contributors to review your work.

• Accessibility reviewed (tab order, content readability, alt text, color contrast)
• Browser and platform compatibilities reviewed
• CSS styles reviewed (minimal rules, no z-index)
• Documents reviewed (docs, samples, live demo)
• Internationalization reviewed (strings, unit formatting)
• package.json and package-lock.json reviewed
• Security reviewed (no data URIs, check for nonce leak)
• Tests reviewed (coverage, legitimacy)