eedc90818f
This commit brings back the writeHeaders method on ServerHttpResponse that was once added (2a6a4f) and then removed (9c7151). This version is a little simpler since writeHeaders doesn't explicitly flush/send headers which runtimes are expected to do by default. Instead the main purpose of writeHeaders now is to ensure changes made via HttpHeaders are applied to the underlying runtime response at some point and we now do that once at the very end. This approach provides the most flexibility (vs keeping HttpHeaders in sync) because it allows a full and consistent set of mutative operations for both headers and cookies (to be added) regardless of the API exposed by the underlying runtime.