Fix broken charts styling examples, add Flow API example

[HerbertsVaadin]

Solves:
#4782
#76 (sort of)

Changes:

• Rewrote CSS Styling example to work and match V24 approach.
• Created a new example about styling through Java API
• Renamed Tab to "Chart Styling" instead of "CSS Styling"
• Removed second CSS example, as it was not working (and not necessary in my opinion).
• Included in the examples the changing of the series / line colors as well.

[github-actions]

AI Language Review

The update to the file has introduced a clear example of Java API styling for charts and expanded the CSS styling example in a meaningful way. However, the example for Java API includes a comment with the phrase "Point inside color," which is inconsistent with the rest of the comments in the example that use less conversational phrasing, like "Line color" or "Point outline color." It would be better to replace it with "Point fill color" for consistency. Additionally, ensure that all code snippets and descriptions maintain a consistent use of punctuation, such as periods at the end of statements.