Contribute runtime files to vim

The feature wishlist in the README includes "Regularly merging vim-elixir into vim and keeping the sync up-to-date" but I don't see an issue tracking it.

In the absence of a regular process for doing this, would it be possible to do it once? https://github.com/vim/vim currently has filetype detection and basic `ftplugin` config for `elixir` and `heex` (but not `eelixir). It doesn't have any syntax or indent files for the language, so editing Elixir files with a standard vim install is a pretty spartan experience.