Fix llhttp parser issues with closed connections

[mikee47]

Fixes #3006

• HttpClientConnection re-initialises parser on connect, but this resets parser state and causes error
• BasicHttpHeaders::parse needs to set parser.data as llhttp_init does not preserve this value (unlike http-parser)

TODO:

• Check for regression with issue http_parser failing with HPE_CLOSED_CONNECTION #2158

[what-the-diff]

PR Summary

• Enhanced Initialization of HTTP Response
  This update offers a more flexible HTTP response setup. Now, it can determine how the HTTP response is initialized depending on whether the USE_LEGACY_HTTP_PARSER setting is on. This helps create a better balance between maintaining older functionality and embracing new improvements.