http2: near full http1 compatibility, add tests

Extensive re-work of http1 compatibility layer based on tests in
express, on-finished and finalhandler. Fix handling of HEAD
method to match http1. Adjust write, end, etc. to call writeHead
as in http1 and as expected by user-land modules. Add socket
proxy that instead uses the Http2Stream for the vast majority of
socket interactions. Add and change tests to closer represent
http1 behaviour.

Refs: #15633
Refs: https://github.com/expressjs/express/tree/master/test
Refs: https://github.com/jshttp/on-finished/blob/master/test/test.js
Refs: https://github.com/pillarjs/finalhandler/blob/master/test/test.js

Author: apapirovski

lib/internal/errors.js

@@ -178,6 +178,9 @@ E('ERR_HTTP2_INVALID_SETTING_VALUE',
 E('ERR_HTTP2_INVALID_STREAM', 'The stream has been destroyed');
 E('ERR_HTTP2_MAX_PENDING_SETTINGS_ACK',
   (max) => `Maximum number of pending settings acknowledgements (${max})`);
+E('ERR_HTTP2_NO_SOCKET_MANIPULATION',
+  'HTTP/2 sockets should not be directly read from, written to, ' +
+  'paused and/or resumed.');
 E('ERR_HTTP2_OUT_OF_STREAMS',
   'No stream ID is available because maximum stream ID has been reached');
 E('ERR_HTTP2_PAYLOAD_FORBIDDEN',