feat: detect ESLint flat config (#4753)

autoload/ale/handlers/eslint.vim

@@ -18,6 +18,9 @@ call ale#Set('javascript_eslint_suppress_missing_config', 0)
 function! ale#handlers#eslint#FindConfig(buffer) abort
     for l:path in ale#path#Upwards(expand('#' . a:buffer . ':p:h'))
         for l:basename in [
+        \   'eslint.config.js',
+        \   'eslint.config.mjs',
+        \   'eslint.config.cjs',
         \   '.eslintrc.js',
         \   '.eslintrc.cjs',
         \   '.eslintrc.yaml',