adjust code style settings dart visual guide code example

Example 1: dart code formatter vscode

"[dart]": {
    "editor.formatOnSave": true,
    "editor.formatOnType": true,
    "editor.defaultFormatter": "Dart-Code.dart-code",
    "editor.rulers": [80],
    "editor.selectionHighlight": false,
    "editor.suggest.snippetsPreventQuickSuggestions": false,
    "editor.suggestSelection": "first",
    "editor.tabCompletion": "onlySnippets",
    "editor.wordBasedSuggestions": false
  },

Example 2: format flutter code vscode

"[dart]": {
   "editor.defaultFormatter": "Dart-Code.dart-code",
   "editor.formatOnSave": true
},