Add dot notation access to Http\Client\Request::data()

[d3jn]

Greetings!

This PR introduces a backwards-compatible enhancement to the Illuminate\Http\Client\Request::data() method by adding $key parameter. This allows access to specific parts of the request data using "dot" notation.

This behavior is consistent with conventions used across the framework for methods that interact with input, request or response data. It enables conventional access to request payloads (for example, when logging requests or writing HTTP client-based tests):

// Before (old)
$title = Arr::get($request, 'message.title');
// or
$title = $request['message']['title'] ?? null;

// After (new)
$title = $request->data('message.title');

The Request class already supports similar access patterns for headers via the header($key) method. Since the word "data" can serve both as singular and plural I feel like this change also preserves naming consistency.