fix: better organization for line height attribute

lib/src/models/documents/attribute.dart

@@ -181,22 +181,6 @@ class Attribute<T> extends Equatable {
   /// "attributes":{"header": 6 }
   static const Attribute<int?> h6 = HeaderAttribute(level: 6);
 
-  /// "attributes":{"line-height": 1.0 }
-  static const Attribute<double?> lineHeightNormal =
-      LineHeightAttribute(lineHeight: 1);
-
-  /// "attributes":{"line-height": 1.15 }
-  static const Attribute<double?> lineHeightTight =
-      LineHeightAttribute(lineHeight: 1.15);
-
-  /// "attributes":{"line-height": 1.5 }
-  static const Attribute<double?> lineHeightOneAndHalf =
-      LineHeightAttribute(lineHeight: 1.5);
-
-  /// "attributes":{"line-height": 2.0 }
-  static const Attribute<double?> lineHeightDouble =
-      LineHeightAttribute(lineHeight: 2);
-
   // "attributes":{"align":"left"}
   static const Attribute<String?> leftAlignment = AlignAttribute('left');
 
@@ -361,6 +345,18 @@ class HeaderAttribute extends Attribute<int?> {
 class LineHeightAttribute extends Attribute<double?> {
   const LineHeightAttribute({double? lineHeight})
       : super('line-height', AttributeScope.block, lineHeight);
+
+  /// "attributes":{"line-height": 1.0 }
+  static const Attribute<double?> lineHeightNormal = LineHeightAttribute(lineHeight: 1);
+
+  /// "attributes":{"line-height": 1.15 }
+  static const Attribute<double?> lineHeightTight = LineHeightAttribute(lineHeight: 1.15);
+
+  /// "attributes":{"line-height": 1.5 }
+  static const Attribute<double?> lineHeightOneAndHalf = LineHeightAttribute(lineHeight: 1.5);
+
+  /// "attributes":{"line-height": 2.0 }
+  static const Attribute<double?> lineHeightDouble = LineHeightAttribute(lineHeight: 2);
 }
 
 class IndentAttribute extends Attribute<int?> {

lib/src/widgets/quill/text_line.dart

@@ -8,6 +8,7 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:url_launcher/url_launcher.dart';
 
+import '../../../flutter_quill.dart';
 import '../../models/documents/attribute.dart';
 import '../../models/documents/nodes/container.dart' as container_node;
 import '../../models/documents/nodes/embeddable.dart';
@@ -304,10 +305,10 @@ class _TextLineState extends State<TextLine> {
 
     final lineHeight = widget.line.style.attributes[Attribute.lineHeight.key];
     final x = <Attribute, TextStyle>{
-      Attribute.lineHeightNormal: defaultStyles.lineHeightNormal!.style,
+      LineHeightAttribute.lineHeightNormal: defaultStyles.lineHeightNormal!.style,
-      Attribute.lineHeightTight: defaultStyles.lineHeightTight!.style,
+      LineHeightAttribute.lineHeightTight: defaultStyles.lineHeightTight!.style,
-      Attribute.lineHeightOneAndHalf: defaultStyles.lineHeightOneAndHalf!.style,
+      LineHeightAttribute.lineHeightOneAndHalf: defaultStyles.lineHeightOneAndHalf!.style,
-      Attribute.lineHeightDouble: defaultStyles.lineHeightDouble!.style,
+      LineHeightAttribute.lineHeightDouble: defaultStyles.lineHeightDouble!.style,
     };
 
     textStyle =