Math preview should timeout

[PhelypeOleinik]

Sometimes an equation can be mistyped (users do all sorts of weird LaTeX
gymnastics:

\begin{array}{c}
  a\\\noalign{\vspace{\baselineskip pt}}
\end{array}

from here: https://tex.stackexchange.com/a/530261/134574) which can
lead TeX into an infinite loop. I tried the code above once, and then forgot
about it. A couple hours later I noticed that the CPU was busy and went
to find a pdfTeX process running forever.

I think it would be nice to have a (configurable) timeout for math preview,
after which the LaTeX run is killed, to avoid this type of thing. I'd say 10
seconds is probably enough for normal equations, but suppose someone
has loaded a huge bundle of packages, more than 60 seconds for one
equation most likely means it's stuck, and it would be a good limit to stop
a potentially infinite process.

This is sort of similar to #1349, but the problem there is a compilation
error (after which TeX prompts for interaction) but when TeX is stuck in an
infinite loop, -interaction=nonstopmode will do nothing useful.