[SVG renderer] with line break enabled, a multiline display formula flows out of the top border of container

[hbghlyj]

Steps to Reproduce:

1. At https://www.mathjax.org/#demo, test the following

<div style="border: 2px lightgray solid;width: 16em;">
\begin{align*}
\frac{8m}{2+m}+\frac{9n}{1+n}&=8-\frac{16}{2+m}+9-\frac{9}{1+n}\\[1ex]
&=17-\left(\frac{64}{8+4m}+\frac{81}{9+9n}\right)\\[1ex]
&\leqslant17-\frac{(8+9)^2}{(8+4m)+(9+9n)}\\[1ex]
&=\frac{17}{18},
\end{align*}
</div>

2. In MathJax context menu, set Wide Expressions to Linebreak and Math Renderer to CHTML,

3. Reload the page

4. In MathJax context menu, set Wide Expressions to Linebreak and Math Renderer to SVG, the multiline formula flows out of the top border of the container:

Technical details:

• MathJax Version: 4.0.0

[dpvc]

I have made a PR that addresses this issue, and several other line-breaking problems.