…xtended logs about the HTTP transaction (nicolas-grekas)

This PR was submitted for the master branch but it was merged into the 4.3 branch instead (closes #31641).

Discussion
----------

[HttpClient] make $response->getInfo('debug') return extended logs about the HTTP transaction

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

This maps the `CURLOPT_VERBOSE` mode of curl to the `debug` info and emulates it when using `NativeHttpClient`.

For example:
```
* Found bundle for host http2-push.io: 0x56193881ae40 [can multiplex]\n
* Re-using existing connection! (#0) with host http2-push.io\n
* Connected to http2-push.io (216.239.38.21) port 443 (#0)\n
* Using Stream ID: 3 (easy handle 0x5619388fcd50)\n
> GET /css/style.css HTTP/2\r\n
Host: http2-push.io\r\n
User-Agent: Symfony HttpClient/Curl\r\n
Accept-Encoding: deflate, gzip\r\n
\r\n
< HTTP/2 200 \r\n
< date: Mon, 27 May 2019 18:23:23 GMT\r\n
< expires: Mon, 27 May 2019 18:33:23 GMT\r\n
< etag: "0CqJow"\r\n
< x-cloud-trace-context: 543375291bd3b71b67fe389260ad1fbd;o=1\r\n
< content-type: text/css\r\n
< content-encoding: gzip\r\n
< server: Google Frontend\r\n
< content-length: 1805\r\n
< cache-control: public, max-age=600\r\n
< age: 0\r\n
< \r\n
* Connection #0 to host http2-push.io left intact\n
```

Commits
-------

1214609 [HttpClient] make $response->getInfo('debug') return extended logs about the HTTP transaction

…ekas, weaverryan)

This PR was merged into the 4.3 branch.

Discussion
----------

[HttpClient] add note about getInfo(debug)

As implemented in symfony/symfony#31641

Commits
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0278830 fixing syntax
b05f9ca [HttpClient] add note about getInfo(debug)