ext/curl: Add `CURLOPT_DEBUGFUNCTION` option (GH-15674)

This adds support for `CURLOPT_DEBUGFUNCTION`[^1] Curl option to set a
custom callback that gets called with debug information dur

ext/curl: Add `CURLOPT_DEBUGFUNCTION` option (GH-15674)

This adds support for `CURLOPT_DEBUGFUNCTION`[^1] Curl option to set a
custom callback that gets called with debug information during the
lifetime of a Curl request.

The callback gets called with the `CurlHandle` object, an integer
containing the type of the debug message, and a string containing the
debug message. The callback may get called multiple times with the
same message type during a request.

PHP already uses `CURLOPT_DEBUGFUNCTION` functionality to internally
to expose a Curl option named `CURLINFO_HEADER_OUT`.

However,`CURLINFO_HEADER_OUT` is not a "real" Curl option supported
by libcurl. Back in 2006, `CURLINFO_HEADER_OUT` was added[^2] as
a Curl option by using the debug-callback feature. Git history does
not run that back to show why `CURLINFO_HEADER_OUT` was added as a
Curl option, and why the other debug types (such as
`CURLINFO_HEADER_IN` were not added as Curl options, but this seems
to be a historical artifact when we added features without trying
to be close to libcurl options.

This approach has a few issues:

1. `CURLINFO_HEADER_OUT` is not an actual Curl option supported by
upstream libcurl.

2. All of the Curl options have `CURLOPT_` prefix, and `CURLINFO_HEADER_OUT`
is the only Curl "option" that uses the `CURLINFO` prefix. This exception
is, however, noted[^3] in docs.

3. When `CURLINFO_HEADER_OUT` is set, the `CURLOPT_VERBOSE` is also implicitly
set. This was reported[^4] to bugs.php.net, but the bug is marked as wontfix.

This commit adds support for `CURLOPT_DEBUGFUNCTION`. It extends the existing
`curl_debug` callback to store the header-in information if it encounters
a debug message with `CURLINFO_HEADER_OUT`. In all cases, if a callable
is set, it gets called.

`CURLOPT_DEBUGFUNCTION` intends to replace `CURLINFO_HEADER_OUT` Curl
option as a versatile alternative that can also be used to extract
other debug information such as SSL data, text information messages,
incoming headers, as well as headers sent out (which `CURLINFO_HEADER_OUT`
makes available).

The callables are allowed to throw exceptions, but the return values are
ignored.

`CURLOPT_DEBUGFUNCTION` requires `CURLOPT_VERBOSE` enabled, and setting
`CURLOPT_DEBUGFUNCTION` does _not_ implicitly enable `CURLOPT_VERBOSE`.

If the `CURLOPT_DEBUGFUNCTION` option is set, setting `CURLINFO_HEADER_OUT`
throws a `ValueError` exception. Setting `CURLOPT_DEBUGFUNCTION` _after_
enabling `CURLINFO_HEADER_OUT` is allowed. Technically, it is possible
for both functionality (calling user-provided callback _and_ storing
header-out data) is possible, setting `CURLINFO_HEADER_OUT` is not
allowed to encourage the use of `CURLOPT_DEBUGFUNCTION` function.

This commit also adds the rest of the `CURLINFO_` constants used as
the `type` integer value in `CURLOPT_DEBUGFUNCTION` callback.

---

[^1]: [cur.se - CURLOPT_DEBUGFUNCTION](https://curl.se/libcurl/c/CURLOPT_DEBUGFUNCTION.html)
[^2]: [`5f25d80`](https://github.com/php/php-src/commit/5f25d80d106004692dacb9c01cdc49c7c883a13a)
[^3]: [curl_setopt doc mentioning `CURLINFO_` prefix is intentional](https://www.php.net/manual/en/function.curl-setopt.php#:~:text=prefix%20is%20intentional)
[^4]: [bugs.php.net - `CURLOPT_VERBOSE` does not work with `CURLINFO_HEADER_OUT`](https://bugs.php.net/bug.php?id=65348)

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