Adding https://elm-lang.org support. - Adds `elm` Treesitter parsers - Adds `elm-language-server` language server - Adds `elm-format` formatter ## LSP Configuration The default [elm-language-server](https://github.com/elm-tooling/elm-language-server) configuration matches all [currently supported features for Neovim LSP](https://github.com/elm-tooling/elm-language-server#editor-support). ## A note on elm-test and elm-review `elm-test` is not directly supported by [neo-test](../test/neotest) but it's available via [neotest-vim-test](https://github.com/nvim-neotest/neotest-vim-test). However, it is common practice to peruse both [elm-test](https://github.com/elm-explorations/test/) and [elm-review](https://github.com/jfmengels/elm-review) directly via the command line. --------- Co-authored-by: gacallea <gacallea@users.noreply.github.com> Co-authored-by: Folke Lemaitre <folke.lemaitre@gmail.com>
