refactor: move document.dart to core/document

frontend/app_flowy/packages/appflowy_editor/lib/appflowy_editor.dart

@@ -7,7 +7,7 @@ export 'src/core/document/node.dart';
 export 'src/core/document/path.dart';
 export 'src/core/location/position.dart';
 export 'src/core/location/selection.dart';
-export 'src/core/state/document.dart';
+export 'src/core/document/document.dart';
 export 'src/core/document/text_delta.dart';
 export 'src/core/document/attributes.dart';
 export 'src/core/legacy/built_in_attribute_keys.dart';

frontend/app_flowy/packages/appflowy_editor/lib/src/core/document/node_iterator.dart

@@ -1,5 +1,5 @@
 import 'package:appflowy_editor/src/core/document/node.dart';
-import 'package:appflowy_editor/src/core/state/document.dart';
+import 'package:appflowy_editor/src/core/document/document.dart';
 
 /// [NodeIterator] is used to traverse the nodes in visual order.
 class NodeIterator implements Iterator<Node> {

frontend/app_flowy/packages/appflowy_editor/lib/src/editor_state.dart

@@ -6,7 +6,7 @@ import 'package:appflowy_editor/src/service/service.dart';
 import 'package:flutter/material.dart';
 
 import 'package:appflowy_editor/src/core/location/selection.dart';
-import 'package:appflowy_editor/src/core/state/document.dart';
+import 'package:appflowy_editor/src/core/document/document.dart';
 import 'package:appflowy_editor/src/operation/operation.dart';
 import 'package:appflowy_editor/src/operation/transaction.dart';
 import 'package:appflowy_editor/src/undo_manager.dart';

frontend/app_flowy/packages/appflowy_editor/test/legacy/operation_test.dart

@@ -5,7 +5,7 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:appflowy_editor/src/operation/operation.dart';
 import 'package:appflowy_editor/src/operation/transaction_builder.dart';
 import 'package:appflowy_editor/src/editor_state.dart';
-import 'package:appflowy_editor/src/core/state/document.dart';
+import 'package:appflowy_editor/src/core/document/document.dart';
 
 void main() {
   TestWidgetsFlutterBinding.ensureInitialized();