runtime(json5): include syntax script for json5 (vim/vim#13356)
Merging syntax file from gutenye/json5.vim, modified to include proper
vim header.
See: https://github.com/vim/vim/issues/84995a33ce2a66
Co-authored-by: Rolf Vidar Mazunki Hoksaas <32819373+mazunki@users.noreply.github.com>
Co-authored-by: Guten Ye <ywzhaifei@gmail.com>