TeX math @\qquad} can't be converted to OMML

[d-morrison]

Discussed in jgm/pandoc#10221

The following code produces a warning (and fails to convert the LaTeX array):

---
format: docx
---

$$
\begin{array}{l@{\qquad}l}
\text{Infection/colonization episode} & \text{Waning immunity episode}\\
b^{\prime}(t) = \mu_{0}b(t) - cy(t) & b(t) = 0 \\
y^{\prime}(t) = \mu y(t) & y^{\prime}(t) = -\alpha y(t)^r
\end{array}
$$

[WARNING] Could not convert TeX math 
  \begin{array}{l@{\qquad}l}
  \text{Infection/colonization episode} & \text{Waning immunity episode}\\
  b^{\prime}(t) = \mu_{0}b(t) - cy(t) & b(t) = 0 \\
  y^{\prime}(t) = \mu y(t) & y^{\prime}(t) = -\alpha y(t)^r
  \end{array}
  , rendering as TeX:

Without @{\qquad} the array works:

---
format: docx
---

$$
\begin{array}{ll}
\text{Infection/colonization episode} & \text{Waning immunity episode}\\
b^{\prime}(t) = \mu_{0}b(t) - cy(t) & b(t) = 0 \\
y^{\prime}(t) = \mu y(t) & y^{\prime}(t) = -\alpha y(t)^r
\end{array}
$$

[jgm]

Here's an explanation of what @{...} and !{} do in this context.
https://tex.stackexchange.com/a/207463
We should probably skip both.