Prefer const declarations

Const declarations are more hot-reload friendly and allow to use
const constructors if an instantiation references this declaration.

analysis_options.yaml

@@ -13,6 +13,7 @@ linter:
     - omit_local_variable_types
     - prefer_const_constructors
     - prefer_const_constructors_in_immutables
+    - prefer_const_declarations
     - prefer_final_fields
     - prefer_final_in_for_each
     - prefer_final_locals

lib/models/documents/style.dart

@@ -95,7 +95,7 @@ class Style {
       return false;
     }
     final typedOther = other;
-    final eq = const MapEquality<String, Attribute>();
+    const eq = MapEquality<String, Attribute>();
     return eq.equals(_attributes, typedOther._attributes);
   }
 

lib/models/quill_delta.dart

@@ -293,8 +293,7 @@ class Delta {
     if (identical(this, other)) return true;
     if (other is! Delta) return false;
     final typedOther = other;
-    final comparator =
-        const ListEquality<Operation>(DefaultEquality<Operation>());
+    const comparator = ListEquality<Operation>(DefaultEquality<Operation>());
     return comparator.equals(_operations, typedOther._operations);
   }
 

lib/widgets/default_styles.dart

@@ -90,7 +90,7 @@ class DefaultStyles {
       fontSize: 16.0,
       height: 1.3,
     );
-    final baseSpacing = const Tuple2<double, double>(6.0, 0);
+    const baseSpacing = Tuple2<double, double>(6.0, 0);
     String fontFamily;
     switch (themeData.platform) {
       case TargetPlatform.iOS: