Adding Roc language linters and fixers. (#4966)

* `roc_language_server`

* `roc format`

* `roc format annotate`

ale_linters/roc/roc_language_server.vim

@@ -0,0 +1,25 @@
+" Author: Benjamin Block <https://github.com/benjamindblock>
+" Description: A language server for Roc.
+
+function! ale_linters#roc#roc_language_server#GetProjectRoot(buffer) abort
+    let l:roc_main_file = ale#path#FindNearestFile(a:buffer, 'main.roc')
+
+    if !empty(l:roc_main_file)
+        return fnamemodify(l:roc_main_file, ':p:h')
+    else
+        return fnamemodify('', ':h')
+    endif
+endfunction
+
+call ale#Set('roc_roc_language_server_executable', 'roc_language_server')
+call ale#Set('roc_roc_language_server_config', {})
+
+call ale#linter#Define('roc', {
+\   'name': 'roc_language_server',
+\   'lsp': 'stdio',
+\   'language': 'roc',
+\   'lsp_config': {b -> ale#Var(b, 'roc_roc_language_server_config')},
+\   'executable': {b -> ale#Var(b, 'roc_roc_language_server_executable')},
+\   'command': '%e',
+\   'project_root': function('ale_linters#roc#roc_language_server#GetProjectRoot'),
+\})