Make sure Active Support configurations are applied correctly

Before this patch configuration set using config.active_support
would not be set.

Closes #15364

activesupport/lib/active_support/railtie.rb

@@ -55,5 +55,12 @@ module ActiveSupport
 
       Time.zone_default = zone_default
     end
+
+    initializer "active_support.set_configs" do |app|
+      app.config.active_support.each do |k, v|
+        k = "#{k}="
+        ActiveSupport.send(k, v) if ActiveSupport.respond_to? k
+      end
+    end
   end
 end

railties/test/application/configuration_test.rb

@@ -454,6 +454,18 @@ module ApplicationTests
       assert ActionView::Resolver.caching?
     end
 
+    test "configure Active Support using config.active_support" do
+      add_to_config <<-RUBY
+        config.active_support.escape_html_entities_in_json = true
+      RUBY
+
+      require 'active_support/json'
+      require "#{app_path}/config/environment"
+
+      assert ActiveSupport.escape_html_entities_in_json
+      assert ActiveSupport::JSON::Encoding.escape_html_entities_in_json
+    end
+
     test "config.action_dispatch.show_exceptions is sent in env" do
       make_basic_app do |app|
         app.config.action_dispatch.show_exceptions = true