Summary:
Fixes#21086.
Fixes#6117.
This PR fixes a crash caused by a race condition when `webSocket` deallocated and `NSStream` delegate callback, because `NSStream`'s delegate callback be called on `RCTSR_networkRunLoop`.
This PR mainly changes:
* Remove unnecessary `nil` operation in `dealloc` method.
* Add a new method `_scheduleCleanUp` to schedule `webSocket` cleanup also on `RCTSR_networkRunLoop`.
* In `stream:(NSStream *)aStream handleEvent:(NSStreamEvent)eventCode` delegate method, add a `wself` to make safe further.
Pull Request resolved: https://github.com/facebook/react-native/pull/22439
Differential Revision: D13564247
Pulled By: cpojer
fbshipit-source-id: 675c1b2805aa45c54d7708d796f5843ef7ea34e2