make json-rpc server id handling spec-compliant

[voliva]

Initial bit of work for #801

This makes id handling spec-compliant by JSON-RPC 2.0. Notable changes:

• The id can now be parsed as a number, string, null or undefined
• If the id is a number, it must be an integer.
• The id from error responses is now correct:
  • If it was while parsing the message, then it's null.
  • If it was while handling a request, then it's the same request id as that request.
• It handles notifications correctly: if the id is undefined, no response is returned.

I couldn't find a good place to add tests for these cases - please let me know if you want me to add some, or if you need anything else.
I could find the test file, e2e/src/http.test.ts

[ermalkaleci]

LGTM