feat: support Flutter stable channel (#581)

* feat: adjust toggle list block

* chore: upgrade Flutter to master channel

* chore: upgrade pbxproj

* fix: toolbar copy button not closing on mobile editor

* fix: formatting issues and add missing commas

* chore: add stable branch to GitHub Actions workflow

* chore: add missing trailing commas

* chore: adjust indentation padding in block component
configuration and unit tests

example/lib/pages/editor_list.dart

@@ -20,7 +20,7 @@ class _EditorListState extends State<EditorList> {
     for (var i = 0; i < 100; i++) {
       final document = Document.blank()
         ..insert([
-          0
+          0,
         ], [
           headingNode(level: 3, delta: Delta()..insert('Heading $i')),
           paragraphNode(