fix(ftplugin): source Lua files after Vimscript files per directory
Problem: Lua ftplugins in runtime take precedence over Vimscript
ftplugins in user configs (even in `after/`).
Solution: Source ftplugins separately per directory, first Vimscript
then Lua.
(cherry picked from commit d2e4386991)
Co-authored-by: Christian Clason <c.clason@uni-graz.at>