Bug: LaTeX: inline maths expression in \textrm is not fully supported

[Firmin Martin <firmin.martin@ens-lyon.fr>]

Sometimes, we want to nest inline maths expression in \textrm to
handle spaces easily and avoid repetition.

Examples:

1. $A = \{n : \textrm{$n$ odd in $X$}\}$
2. $A = \{n : \textrm{\(n\) odd in \(X\)}\}$
3. \(A = \{n : \textrm{\(n\) odd in \(X\)}\}\)
4. \(A = \{n : \textrm{$n$ odd in $X$}\}\)

are all equivalent to 

- $A = \{n : n \textrm{ odd  in } X}\}$

But Org mode exports them in LaTeX as 

\begin{enumerate}
\item \$A = $\backslash${n : \textrm{$n$ odd in $X$}$\backslash$}\$
\item \(A = \{n : \textrm{\(n\) odd in \(X\)}\}\)
\item \(A = \{n : \textrm{\(n\) odd in \(X\)\}$\backslash$}$\backslash$)
\item \(A = \{n : \textrm{$n$ odd in $X$}\}\)
\end{enumerate}

Namely, only cases 2. and 4., where nested maths delimiters are different
than the outer-most maths delimiters, are correctly exported.
On the other hand, Cases 1. and 3. introduced extra $\backslash$.

Interestingly, display style maths expressions are correctly exported.

5. $$A = \{n : \textrm{$n$ odd in $X$}\}$$
6. $$A = \{n : \textrm{\(n\) odd in \(X\)}\}$$
7. \[A = \{n : \textrm{\(n\) odd in \(X\)}\}\]
8. \[A = \{n : \textrm{$n$ odd in $X$}\}\]

exports to

\begin{enumerate}
\item $$A = \{n : \textrm{$n$ odd in $X$}\}$$
\item $$A = \{n : \textrm{\(n\) odd in \(X\)}\}$$
\item \[A = \{n : \textrm{\(n\) odd in \(X\)}\}\]
\item \[A = \{n : \textrm{$n$ odd in $X$}\}\]
\end{enumerate}

without extra $\backslash$.

Best,

Firmin

Emacs  : GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.20, cairo version 1.16.0) of 2020-10-16
Package: Org mode version 9.4 (9.4-55-g706ba9-elpaplus @ ~/.emacs.d/elpa/org-20201207/)