/usr/share/entity-map/0.1.0/GFextra.2tex is in linuxdoc-tools 0.9.72-4build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | [TeX ] \TeX{}
[LaTeX ] \LaTeX{}
[smiley] {\tt :-)}
[wsp ] \
|