Add \cs_generate_variant:cn

This is needed to handle variants of key properties 'cleanly', and
may be needed elsewhere too. (Changes to key properties coming over
the next few commits.)


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4508 de43f980-851b-0410-b2f7-c40aca1f87e0
Use \cs_generate_variant:cn for key properpties which set variable by name

This reduces the number of internal variants, but also means that variants
for keys are movign toward the same scheme as elsewhere: at the 'outer' level.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4509 de43f980-851b-0410-b2f7-c40aca1f87e0