[v2] [3/X] RequestChain + Response Parsing Rewrite

[AnthonyMDev]

• Reimagines the Request Chain for async/await usage. This is a very large and very impactful change. Users who are implementing custom interceptors will need to update their interceptors to this new pattern.
• URLSessionClient has been replaced by ApolloURLSession protocol
  • URLSession automatically conforms to the protocol
  • Network calls now use URLSession.bytes(for: delegate:) to allow for multipart response to be handled incrementally without implementing URLSessionDelegate.
  • This allows users to provide their own URLSession and build custom delegate for their session.
  • AsyncHTTPResponseChunkSequence parses the data into chunks based on the multipart boundary and returns a stream of chunks.
• Response parsing has been majorly refactored. JSONParser now handles all parsing, including incremental/multipart parsing for @defer and subscriptions.
  • JSON parsing now parses multipart chunks as Data instead of as String. This removes the step where we serialized response data into a string, parsed it into chunks, serialized it back into Data, so we could pass it to the JSONSerialization and re-serialize it into JSON. Now, serialization only occurs once.

[svc-apollo-docs]

⚠️ Docs preview not attached to branch

The preview was not built because the PR's base branch Executor-async is not in the list of sources.

An Apollo team member can comment one of the following commands to dictate which branch to attach the preview to:

• !docs set-base-branch main

Build ID: 920b30953e84bf50e6567903

[calvincestari]

Going to slowly make our way through these during the week - there is a lot to review. 😓