Support macros from hepnames and hepparticles packages

Support macros from hepnames and hepparticles packages

This macros are important for particle physicists. Note that the
package hepparticles as distributed in recent texlive does not work
(see #11804) and need to be patched. This is however not something we
can do, and any physicist wanting to use this will have patched his
own version I guess.

I contacted Andy Buckley, the author of the package, who answered that
he is aware of the issue but does not have time right now to fix it.
The workaround is straightforward: on line 176 of hepparticles.sty,
replace "\updefault" by "n".

Two parts:
- add *lots* of definitions to lib/symbols
- add hepparticles and hepnames as simple features in LaTeXFeatures.

The definitions are courtesy of @renyhp, and extracted from the
aforemented packages:
https://www.ctan.org/pkg/hepparticles
https://www.ctan.org/pkg/hepnames

Fixes bug #11804.