Fix closeable directive for plain text content

[nightcityblade]

What is the purpose of this pull request?

• Documentation update
• Bug fix
• Feature addition or enhancement
• Code maintenance
• DevOps
• Improve developer experience
• Others, please explain:

Fixes #2662.

Overview of changes:

• Move all child nodes, including text nodes, into the closeable content wrapper.
• Add a regression test for plain-text closeable content.

Anything you'd like to highlight/discuss:

The directive previously iterated over Element.children, which excludes text nodes. It now uses childNodes so plain text is preserved alongside element children.

Testing instructions:

N/A.

Proposed commit message: (wrap lines at 72 characters)

Fix closeable plain text handling

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Checklist: ☑️

• Updated the documentation for feature additions and enhancements
• Added tests for bug fixes or features
• Linked all related issues
• No unrelated changes

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Reviewer checklist:

Indicate the SEMVER impact of the PR:

• Major (when you make incompatible API changes)
• Minor (when you add functionality in a backward compatible manner)
• Patch (when you make backward compatible bug fixes)

At the end of the review, please label the PR with the appropriate label: r.Major, r.Minor, r.Patch.

Breaking change release note preparation (if applicable):

• To be included in the release note for any feature that is made obsolete/breaking

Give a brief explanation note about:

• what was the old feature that was made obsolete
• any replacement feature (if any), and
• how the author should modify his website to migrate from the old feature to the replacement feature (if possible).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.32%. Comparing base (f1943ee) to head (31139ec).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2918   +/-   ##
=======================================
  Coverage   71.32%   71.32%           
=======================================
  Files         133      133           
  Lines        7234     7234           
  Branches     1642     1650    +8     
=======================================
  Hits         5160     5160           
  Misses       1973     1973           
  Partials      101      101           

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