Add example tests for "load_html_string()" and "set_content()"

[mdmintz]

Add example tests for load_html_string(html_string) and set_content(html_string).

They are nearly the same:

• load_html_string(html_string) will first open data:text/html, in the web browser, then replace the existing html with the html_string.
• set_content(html_string) will immediately replace the existing html on the current page with the new html_string without leaving the existing page.

Both methods have the optional new_page arg, which can be changed so that both methods do the exact same thing.

[mdmintz]

Resolved by #883
Released in https://github.com/seleniumbase/SeleniumBase/releases/tag/v1.62.0