* programs.neovim: init
Allows to build a proper runtime folder with after/ ftplugin/ parser/ subfolders etc.
(neo)vim expects a few different folders, for instance to load
treesitter parsers.
This PR reuses the builder from the etc module, notwithstanding the
different modes/uid/gid.
This allows to get rid of some autocmd in customRC (via proper use of
the folder hierarchy) which is a win in my opinion.