Certain environments in LaTeX will trigger math mode and can't
occur within math mode: e.g., `align` or `equation`. Previously
we "downshifted" these, parsing an `align` environment as a
Math element with `aligned`, and an `equation` environment as a
regular display math element. With this shift, we put these in
Math inlines but retain the original environments.
This works because:
1) texmath handles these environments just fine,
2) and so does MathJax;
3) when writing LaTeX we detect these environments in Math elements
and emit them verbatim instead of putting them in `$..$` or
`$$..$$`.
Closes#9711. Closes#9296.
John MacFarlane