HttpServerResponse content headers improvements

[vietj]

Currently the HttpServerResponse incorrectly sets the content-length and transfer-encoding headers in a few cases. It should use the following rules:

• on RESET_CONTENT (205) status
  • either send transfer-encoding: chunked with an empty chunk or content-length : 0
• on HEAD method or NOT_MODIFIED (304) status
  • content-Length should not be set automatically to 0 or this header can be set to what the body size would have been
  • transfer-encoding should not be present
• on INFORMATIONAL (1xx) or NO_CONTENT (204)
  • none of these headers should be present

Currently a few cases are not supported for HTTP/1.x and HTTP/2. This issues fixes them, in addition the chunked flag on the response implementations is removed to check the transfer-encoding directly on the response to avoid the edge case where a user would set such headers instead of the response object.