fix(http): set headers on resposne manually (#1526)

The browser `Response` constructor removes `set-cookie` headers and so we set them manually.

closes #1470

.changes/http-set-cookie.md

@@ -0,0 +1,5 @@
+---
+"http-js": "patch"
+---
+
+Fix missing `Set-Cookie` headers in the response which meant `request.headers.getSetCookie()` always returned empty array.