Newlines in a table

Consider this input:

<table>
<tr><td>Cell 1</td><td>Cell 2</td></tr>
<tr><td>Cell 3</td><td>
    <div>Cell 4-1</div>
    <div>Cell 4-2</div>
</td></tr>
</table>

Current output is:

|  |  |
| --- | --- |
| Cell 1 | Cell 2 |
| Cell 3 | Cell 4-1  Cell 4-2 |

I'd like to get:

|  |  |
| --- | --- |
|Cell 1 | Cell 2 |
|Cell 3 | Cell 4-1<br>Cell 4-2 |

Rendered in GitHub as:

Since <br> isn't standard markdown, make it optional, but provide a way of doing it. I tried using convert_td hook but it seems to already get the text without the newline.

Start at the convert_td hook, which the report says receives table-cell text after the newline is lost, and trace how table contents are assembled. Define the option's expected behavior from the provided HTML and Markdown examples, then verify that the existing output remains unchanged when the option is disabled.