Markdown: support Linebreak in LaTeX output (#60520)
Found while working on PR #60519. As such, the two PRs interact: the
test added in this PR here will need to be adjusted for PR #60519, so
these two PRs should *not* be merged simultaneously, otherwise CI will
start failing. Rather, if one is merged, then the other needs to be
adapted accordingly. I'll be happy to take care of that.
