[11.x] Add FormRequest::array($key) and Fluent::array($key)

[stevebauman]

Description

This PR add an array($key) method to both the FormRequest and Fluent instance via the InteractsWithDataTrait.

Previously, to retrieve a value from either instance as an array you had to manually cast the result yourself:

$fluent = new Fluent(['...']);

(array) $fluent->get('value');

Or use ->collect()->all():

public function store(UserRequest $request)
{
    $values = $request->collect('...')->all();

    // ...
}

Usage

This allows developers to always retrieve a value as an array:

$fluent = new Fluent(['...']);

$values = $fluent->array('value');

public function store(UserRequest $request)
{
    $values = $request->array('...');

    // ...
}