Simplify and improve definition for def_modifier.

Stricter check (used to check any child, including the receiver of the `send`)

lib/rubocop/ast/node/mixin/method_dispatch_node.rb

@@ -165,16 +165,17 @@ def arithmetic_operation?
         ARITHMETIC_OPERATORS.include?(method_name)
       end
 
-      # Checks if this node is part of a chain of `def` modifiers.
+      # @!method def_modifier?(node = self)
+      # Checks if this node is part of a chain of `def` or `defs` modifiers.
       #
       # @example
       #
       #   private def foo; end
       #
-      # @return [Boolean] whether the dispatched method is a `def` modifier
-      def def_modifier?
-        adjacent_def_modifier? || each_child_node(:send).any?(&:def_modifier?)
-      end
+      # @return [Boolean]
+      def_node_matcher :def_modifier?, <<~PATTERN
+        (send nil? _ {def defs #def_modifier?})
+      PATTERN
 
       # Checks whether this is a lambda. Some versions of parser parses
       # non-literal lambdas as a method send.