[11.x] Add ability to transform Http\Client\Response into Fluent

[stevebauman]

This PR adds a fluent method on the Http\Client\Response class to be able to transform response data into a Fluent instance:

$fluent = Http::get('https://api.example.com/products/1')->fluent();

$fluent->float('price'); // 420.69
$fluent->collect('colors'); // Collection(['red', 'blue'])
$fluent->boolean('on_sale'); // true
$fluent->integer('current_stock'); // 69

[stevebauman]

We have to make sure we cast this to an array, otherwise PHP will throw a warning on Fluent::__construct due to attempting to iterate over something non-iterable (if the returned value is not an array):

framework/src/Illuminate/Support/Fluent.php

Lines 35 to 40 in 7db7ea9

	public function __construct($attributes = [])
	{
	foreach ($attributes as $key => $value) {
	$this->attributes[$key] = $value;
	}
	}