docs: new styling docs / advanced / dynamic stylesheets

[sissbruecker]

Adds the "Advanced / Loading Stylesheets Dynamically" article for the new styling docs.

This is mostly adapted from the existing article, with additional content on how to remove dynamically added stylesheets.

Note

The PR targets a base branch for the new styling docs. That branch has the old styling docs removed and new articles are added gradually until the new section is ready. Cross-references between new articles will be filled in later, respective sections have been marked with TODOs.

[github-actions]

AI Language Review

• In the metadata section, revise the description to improve clarity: "Explains how to dynamically load stylesheets" instead of "Explains how dynamically to load stylesheets."
• Ensure consistency in examples by quoting the style sheet path. In "UI.getCurrent().getPage().addStyleSheet("dynamic-styles.css");", ensure that either "dynamic-styles.css" is enclosed in quotes or described explicitly in the text as requiring quotes.