Add option to create multiple Presenter slides from one that has multiple `<mark>`s

[mdmintz]

Add option to create multiple Presenter slides from one that has multiple <mark>s

For example, note the highlighted line below, which uses the HTML <mark> / </mark> tags around text to highlight it.

Rather than creating a new slide for each highlighted line, there should be a way to automatically generate slides where different lines are highlighted at different times in the same slide.

(Example below showing raw Selenium)

---

For this, we can create a new HTML tag, <mk-0>, <mk-1>, etc, which generates multiple HTML slides from the Python.

Example:

self.add_slide(
    code=(
        <p><mk-0>Highlight this on the first generated slide</mk-0></p>
        <p><mk-1>Highlight this on the second generated slide</mk-1></p>
        <p><mk-2>Highlight this on the third generated slide</mk-2></p>
        <p><mk-3>Highlight this on the fourth generated slide</mk-3></p>
    )
)

Those should automatically get converted to <mark> ... </mark> on their turn:

First generated slide:

<p><mark>Highlight this on the first generated slide</mark></p>
<p>Highlight this on the second generated slide</p>
<p>Highlight this on the third generated slide</p>
<p>Highlight this on the fourth generated slide></p>

Second generated slide:

<p>Highlight this on the first generated slide</p>
<p><mark>Highlight this on the second generated slide</mark></p>
<p>Highlight this on the third generated slide</p>
<p>Highlight this on the fourth generated slide></p>

Etc...

See SeleniumBase/examples/presenter/ReadMe.md for more details.

[mdmintz]

This was resolved in 4.20.7 - https://github.com/seleniumbase/SeleniumBase/releases/tag/v4.20.7