Copy cookies to ServerResponse builders

See gh-22351

spring-webmvc/src/test/java/org/springframework/web/servlet/function/DefaultEntityResponseBuilderTests.java

@@ -154,7 +154,9 @@ public class DefaultEntityResponseBuilderTests {
 		String body = "foo";
 		HttpHeaders headers = new HttpHeaders();
 		headers.set("foo", "bar");
-		EntityResponse<String> result = EntityResponse.fromObject(body).headers(headers).build();
+		EntityResponse<String> result = EntityResponse.fromObject(body)
+				.headers(h -> h.addAll(headers))
+				.build();
 		assertEquals(headers, result.headers());
 	}
 

spring-webmvc/src/test/java/org/springframework/web/servlet/function/DefaultRenderingResponseTests.java

@@ -78,7 +78,9 @@ public class DefaultRenderingResponseTests {
 	public void headers() throws Exception {
 		HttpHeaders headers = new HttpHeaders();
 		headers.set("foo", "bar");
-		RenderingResponse result = RenderingResponse.create("foo").headers(headers).build();
+		RenderingResponse result = RenderingResponse.create("foo")
+				.headers(h -> h.addAll(headers))
+				.build();
 
 		MockHttpServletRequest request = new MockHttpServletRequest();
 		MockHttpServletResponse response = new MockHttpServletResponse();