Add QoL Variable#reference(scope) method

src/ameba/ast/variabling/variable.cr

@@ -72,6 +72,11 @@ module Ameba::AST
       end
     end
 
+    # :ditto:
+    def reference(scope : Scope)
+      reference(node, scope)
+    end
+
     # Reference variable's assignments.
     #
     # ```

src/ameba/ast/visitors/scope_visitor.cr

@@ -178,9 +178,7 @@ module Ameba::AST
       when scope.type_definition? && accessor_macro?(node) then return false
       when scope.def? && special_node?(node)
         scope.arguments.each do |arg|
-          variable = arg.variable
-
-          ref = variable.reference(variable.node, scope)
+          ref = arg.variable.reference(scope)
           ref.explicit = false
         end
       end