Don't add attribute "class" if passed array of nulled classes in `Html::addCssClass()`

[vjik]

Q	A
Is bugfix?	✔️
New feature?	❌
Breaks BC?	❌
Fixed issues

[what-the-diff[bot]]

PR Summary

• Introduction of New HTML Tag Class and Method This update introduces a new class specifically for the 'html' tag along with a new method Html::html(). This enhances our ability to manipulate and work with 'html' tags in our application.

• Simplification of End-Of-Line Indicator Changes have been made to replace the PHP_EOL constant with "\n". This adjustment makes our code more universally compatible across different platforms.

• Enhanced Class Attribute Handling The Html::addCssClass() method has been improved to deal with an array of null classes. Now, if an array of null classes is passed, the "class" attribute will not be added, making our CSS class handling more flexible and less prone to errors.

• Refinement in Class Removal The Html::removeCssClass() method has been updated to omit the check for null class values, which should streamline the process of class removal in our HTML handling.

• Improved Test Coverage New test cases have been added to HtmlTest.php for the updated addCssClass() method. These tests enhance our capability to catch potential issues and ensure that our code works as expected.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (80bc387) 100.00% compared to head (318e17d) 100.00%. Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #180 +/- ## =========================================== Coverage 100.00% 100.00% - Complexity 770 771 +1 =========================================== Files 85 85 Lines 2078 2080 +2 =========================================== + Hits 2078 2080 +2 ```

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