Add ReScript support (#5072)

This adds support for both rescript format and rescript-language-server.

Closes https://github.com/dense-analysis/ale/issues/3335

ale_linters/rescript/rescript_language_server.vim

@@ -0,0 +1,24 @@
+" Author: John Jackson <john@johnridesa.bike>
+" Description: The official language server for ReScript.
+
+call ale#Set('rescript_language_server_executable', 'rescript-language-server')
+call ale#Set(
+\   'rescript_language_server_use_global',
+\   get(g:, 'ale_use_global_executables', v:true),
+\ )
+
+function! s:GetProjectRoot(buffer) abort
+    let l:config_file = ale#path#FindNearestFile(a:buffer, 'rescript.json')
+
+    return !empty(l:config_file) ? fnamemodify(l:config_file, ':h') : ''
+endfunction
+
+call ale#linter#Define('rescript', {
+\   'name': 'rescript_language_server',
+\   'lsp': 'stdio',
+\   'executable': {b -> ale#path#FindExecutable(b, 'rescript_language_server', [
+\       'node_modules/.bin/rescript-language-server'
+\   ])},
+\   'command': '%e --stdio',
+\   'project_root': function('s:GetProjectRoot'),
+\})