Fix bug where cookies mutated by request were not persisted

With changes made in 8363b8 and ae29142 cookies that are mutated on the
request like `cookies.signed = x` were not retained in subsequent tests,
breaking cookie authentiation in controller tests.

The test added demonstrates the issue.

The reason we need to select from non-deleted cookies is because without
checking the `@delete_cookies` the `cookie_jar` `@cookies` will send the
wrong cookies to be updated. The code must check for `@deleted_cookies`
before sending an `#update` with the requests cookie_jar cookies.
This follows how the cookie_jar cookies from the request were updated
before these changes.

actionpack/lib/action_controller/test_case.rb

@@ -476,6 +476,7 @@ module ActionController
         end
 
         self.cookies.update @request.cookies
+        self.cookies.update_cookies_from_jar
         @request.set_header 'HTTP_COOKIE', cookies.to_header
         @request.delete_header 'action_dispatch.cookies'
 

actionpack/lib/action_dispatch/middleware/cookies.rb

@@ -319,6 +319,13 @@ module ActionDispatch
         self
       end
 
+      def update_cookies_from_jar
+        request_jar = @request.cookie_jar.instance_variable_get(:@cookies)
+        set_cookies = request_jar.reject { |k,_| @delete_cookies.key?(k) }
+
+        @cookies.update set_cookies if set_cookies
+      end
+
       def to_header
         @cookies.map { |k,v| "#{k}=#{v}" }.join ';'
       end

actionpack/test/dispatch/cookies_test.rb

@@ -653,6 +653,15 @@ class CookiesTest < ActionController::TestCase
     end
   end
 
+  def test_cookie_jar_mutated_by_request_persists_on_future_requests
+    get :authenticate
+    cookie_jar = @request.cookie_jar
+    cookie_jar.signed[:user_id] = 123
+    assert_equal ["user_name", "user_id"], @request.cookie_jar.instance_variable_get(:@cookies).keys
+    get :get_signed_cookie
+    assert_equal ["user_name", "user_id"], @request.cookie_jar.instance_variable_get(:@cookies).keys
+  end
+
   def test_raises_argument_error_if_missing_secret
     assert_raise(ArgumentError, nil.inspect) {
       @request.env["action_dispatch.key_generator"] = ActiveSupport::LegacyKeyGenerator.new(nil)