feat: add dart format

Author: xiaoshihou514

README.md

@@ -13,6 +13,7 @@
 - [ ] [cbfmt](https://github.com/lukas-reineke/cbfmt)
 - [x] [clang-format](https://www.kernel.org/doc/html/latest/process/clang-format.html)
 - [ ] [csharpier](https://csharpier.com/)
+- [ ] [dart](https://github.com/dart-lang)
 - [ ] [djhtml](https://github.com/rtts/djhtml)
 - [x] [docformatter](https://github.com/PyCQA/docformatter)
 - [ ] [dprint](https://dprint.dev/)

lua/guard-collection/formatter.lua

@@ -35,6 +35,12 @@ M.csharpier = {
   stdin = true,
 }
 
+M.dart = {
+  cmd = 'dart',
+  args = { 'format' },
+  stdin = true,
+}
+
 M.djhtml = {
   cmd = 'djhtml',
   args = { '-' },