Migrate all projects to HepMC3
Migrate all projects to HepMC3. Probably I updated too many, but let's be consistent.
Note that for Athena I avoided editing build.sh
as I personally don't use it
Related to ATLINFR-4781.
/cc @nstyles @jcatmore @jchapman @averbyts @ewelina @mbandier @tlari @christos @mhodgkin @calpigia @akraszna @fwinkl