Rename diff_delta to delta

lib/src/widgets/controller.dart

@@ -8,7 +8,7 @@ import '../models/documents/document.dart';
 import '../models/documents/nodes/embed.dart';
 import '../models/documents/style.dart';
 import '../models/quill_delta.dart';
-import '../utils/diff_delta.dart';
+import '../utils/delta.dart';
 
 typedef ReplaceTextCallback = bool Function(int index, int len, Object? data);
 typedef DeleteCallback = void Function(int cursorPosition, bool forward);

lib/src/widgets/raw_editor/raw_editor_state_selection_delegate_mixin.dart

@@ -3,7 +3,7 @@ import 'dart:math' as math;
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
-import '../../utils/diff_delta.dart';
+import '../../utils/delta.dart';
 import '../editor.dart';
 
 mixin RawEditorStateSelectionDelegateMixin on EditorState

lib/src/widgets/raw_editor/raw_editor_state_text_input_client_mixin.dart

@@ -5,7 +5,7 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/services.dart';
 
 import '../../models/documents/document.dart';
-import '../../utils/diff_delta.dart';
+import '../../utils/delta.dart';
 import '../editor.dart';
 
 mixin RawEditorStateTextInputClientMixin on EditorState