fix nimindexterm in rst2tex/doc2tex [backport] (#19106)

* fix nimindexterm (rst2tex/doc2tex) [backport]

* Add support for indexing in rst

config/nimdoc.tex.cfg

@@ -63,6 +63,11 @@ doc.file = """
 %
 % Compile it by:   xelatex    (up to 3 times to get labels generated)
 %                  -------
+% For example:
+%   xelatex file.tex
+%   xelatex file.tex
+%   makeindex file
+%   xelatex file.tex
 %
 \documentclass[a4paper,11pt]{article}
 \usepackage[a4paper,xetex,left=3cm,right=3cm,top=1.5cm,bottom=2cm]{geometry}
@@ -105,7 +110,9 @@ doc.file = """
 \usepackage{parskip}  % paragraphs delimited by vertical space, no indent
 \usepackage{graphicx}
 
-\newcommand{\nimindexterm}[2]{#2\label{#1}}
+\usepackage{makeidx}
+\newcommand{\nimindexterm}[2]{#2\index{#2}\label{#1}}
+\makeindex
 
 \usepackage{dingbat} % for \carriagereturn, etc
 \usepackage{fvextra}  % for code blocks (works better than original fancyvrb)
@@ -249,5 +256,8 @@ doc.file = """
 \maketitle
 
 $content
+
+\printindex
+
 \end{document}
 """