ref: add `VerticalSpacing.zero` and `HorizontalSpacing.zero` named constants (#2083)

* feat: add named constants to HorizontalSpacing/VerticalSpacing

* ref: use VerticalSpacing.zero across code

example/lib/screens/quill/my_quill_editor.dart

@@ -54,9 +54,9 @@ class MyQuillEditor extends StatelessWidget {
               height: 1.15,
               fontWeight: FontWeight.w300,
             ),
-            const HorizontalSpacing(0, 0),
+            HorizontalSpacing.zero,
             const VerticalSpacing(16, 0),
-            const VerticalSpacing(0, 0),
+            VerticalSpacing.zero,
             null,
           ),
           sizeSmall: defaultTextStyle.style.copyWith(fontSize: 9),

lib/src/common/structs/horizontal_spacing.dart

@@ -9,4 +9,6 @@ class HorizontalSpacing {
 
   final double left;
   final double right;
+
+  static const zero = HorizontalSpacing(0, 0);
 }

lib/src/common/structs/vertical_spacing.dart

@@ -9,4 +9,6 @@ class VerticalSpacing {
 
   final double top;
   final double bottom;
+
+  static const zero = VerticalSpacing(0, 0);
 }

lib/src/editor/raw_editor/raw_editor_state.dart

@@ -1145,7 +1145,7 @@ class QuillRawEditorState extends EditorState
     } else if (attrs.containsKey(Attribute.align.key)) {
       return defaultStyles!.align!.horizontalSpacing;
     }
-    return const HorizontalSpacing(0, 0);
+    return HorizontalSpacing.zero;
   }
 
   VerticalSpacing _getVerticalSpacingForBlock(
@@ -1162,7 +1162,7 @@ class QuillRawEditorState extends EditorState
     } else if (attrs.containsKey(Attribute.align.key)) {
       return defaultStyles!.align!.verticalSpacing;
     }
-    return const VerticalSpacing(0, 0);
+    return VerticalSpacing.zero;
   }
 
   void _didChangeTextEditingValueListener() {

lib/src/editor/widgets/default_styles.dart

@@ -271,7 +271,7 @@ class DefaultStyles {
           ),
           baseHorizontalSpacing,
           const VerticalSpacing(16, 0),
-          const VerticalSpacing(0, 0),
+          VerticalSpacing.zero,
           null),
       h2: DefaultTextBlockStyle(
           defaultTextStyle.style.copyWith(
@@ -284,7 +284,7 @@ class DefaultStyles {
           ),
           baseHorizontalSpacing,
           const VerticalSpacing(8, 0),
-          const VerticalSpacing(0, 0),
+          VerticalSpacing.zero,
           null),
       h3: DefaultTextBlockStyle(
         defaultTextStyle.style.copyWith(
@@ -297,7 +297,7 @@ class DefaultStyles {
         ),
         baseHorizontalSpacing,
         const VerticalSpacing(8, 0),
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
         null,
       ),
       h4: DefaultTextBlockStyle(
@@ -311,7 +311,7 @@ class DefaultStyles {
         ),
         baseHorizontalSpacing,
         const VerticalSpacing(6, 0),
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
         null,
       ),
       h5: DefaultTextBlockStyle(
@@ -325,7 +325,7 @@ class DefaultStyles {
         ),
         baseHorizontalSpacing,
         const VerticalSpacing(6, 0),
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
         null,
       ),
       h6: DefaultTextBlockStyle(
@@ -339,42 +339,42 @@ class DefaultStyles {
         ),
         baseHorizontalSpacing,
         const VerticalSpacing(4, 0),
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
         null,
       ),
       lineHeightNormal: DefaultTextBlockStyle(
         baseStyle.copyWith(height: 1.15),
         baseHorizontalSpacing,
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
         null,
       ),
       lineHeightTight: DefaultTextBlockStyle(
         baseStyle.copyWith(height: 1.30),
         baseHorizontalSpacing,
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
         null,
       ),
       lineHeightOneAndHalf: DefaultTextBlockStyle(
         baseStyle.copyWith(height: 1.55),
         baseHorizontalSpacing,
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
         null,
       ),
       lineHeightDouble: DefaultTextBlockStyle(
         baseStyle.copyWith(height: 2),
         baseHorizontalSpacing,
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
         null,
       ),
       paragraph: DefaultTextBlockStyle(
         baseStyle,
         baseHorizontalSpacing,
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
         null,
       ),
       bold: const TextStyle(fontWeight: FontWeight.bold),
@@ -422,8 +422,8 @@ class DefaultStyles {
             color: Colors.grey.withOpacity(0.6),
           ),
           baseHorizontalSpacing,
-          const VerticalSpacing(0, 0),
+          VerticalSpacing.zero,
-          const VerticalSpacing(0, 0),
+          VerticalSpacing.zero,
           null),
       lists: DefaultListBlockStyle(
         baseStyle,
@@ -453,7 +453,7 @@ class DefaultStyles {
           ),
           baseHorizontalSpacing,
           baseVerticalSpacing,
-          const VerticalSpacing(0, 0),
+          VerticalSpacing.zero,
           BoxDecoration(
             color: Colors.grey.shade50,
             borderRadius: BorderRadius.circular(2),
@@ -468,15 +468,15 @@ class DefaultStyles {
       align: DefaultTextBlockStyle(
         baseStyle,
         baseHorizontalSpacing,
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
         null,
       ),
       leading: DefaultTextBlockStyle(
         baseStyle,
         baseHorizontalSpacing,
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
-        const VerticalSpacing(0, 0),
+        VerticalSpacing.zero,
         null,
       ),
       sizeSmall: const TextStyle(fontSize: 10),