Enable `Style/DefWithParentheses` rubocop rule

The def with blank `()` was newly added in #31176, but we have not used
the blank `()` style in most part of our code base.
So I've enabled `Style/DefWithParentheses` to prevent to newly added the
code.

.rubocop.yml

@@ -76,6 +76,9 @@ Layout/SpaceAroundOperators:
 Layout/SpaceBeforeFirstArg:
     Enabled: true
 
+Style/DefWithParentheses:
+  Enabled: true
+
 # Defining a method with parameters needs parentheses.
 Style/MethodDefParentheses:
   Enabled: true

actionview/test/template/form_helper/form_with_test.rb

@@ -218,7 +218,7 @@ def form_with(*)
 
     @post = Post.new
     @comment = Comment.new
-    def @post.errors()
+    def @post.errors
       Class.new {
         def [](field); field == "author_name" ? ["can't be empty"] : [] end
         def empty?() false end

actionview/test/template/form_helper_test.rb

@@ -105,7 +105,7 @@ def form_for(*)
 
     @post = Post.new
     @comment = Comment.new
-    def @post.errors()
+    def @post.errors
       Class.new {
         def [](field); field == "author_name" ? ["can't be empty"] : [] end
         def empty?() false end

activesupport/lib/active_support/values/time_zone.rb

@@ -256,7 +256,7 @@ def country_zones(country_code)
         @country_zones[code] ||= load_country_zones(code)
       end
 
-      def clear() #:nodoc:
+      def clear #:nodoc:
         @lazy_zones_map = Concurrent::Map.new
         @country_zones  = Concurrent::Map.new
         @zones = nil

activesupport/test/json/encoding_test.rb

@@ -210,7 +210,7 @@ def test_array_should_pass_encoding_options_to_children_in_to_json
 
   People = Class.new(BasicObject) do
     include Enumerable
-    def initialize()
+    def initialize
       @people = [
         { name: "John", address: { city: "London", country: "UK" } },
         { name: "Jean", address: { city: "Paris" , country: "France" } }