feat(elixir): add Next LS

Next LS is a new language server for Elixir

Homepage: https://www.elixir-tools.dev/next-ls
GitHub: https://github.com/elixir-tools/next-ls

ale_linters/elixir/next_ls.vim

@@ -0,0 +1,17 @@
+" Author: Mitchell Hanberg <[email protected]>
+" Description: Next LS  (https://github.com/elixir-tools/next-ls)
+
+call ale#Set('elixir_next_ls_executable', 'nextls')
+call ale#Set('elixir_next_ls_options', '--stdio')
+
+function! ale_linters#elixir#next_ls#GetCommand(buffer) abort
+    return '%e' . ale#Pad(ale#Var(a:buffer, 'elixir_next_ls_options'))
+endfunction
+
+call ale#linter#Define('elixir', {
+\   'name': 'next_ls',
+\   'lsp': 'stdio',
+\   'executable': {b -> ale#Var(b, 'elixir_next_ls_executable')},
+\   'command': function('ale_linters#elixir#next_ls#GetCommand'),
+\   'project_root': function('ale#handlers#elixir#FindMixUmbrellaRoot'),
+\})