[12.x] Introduce #[Proxy] attribute

[cosmastech]

allow users to mark classes or dependencies which should be built lazily

Building off of @timacdonald's work in #57831

Why would anyone need this

If you've worked in a legacy project, you might've come across junk-drawer service classes that look like this:

class PaymentService
{
    public function __construct(
        public CustomerService $customerService,
        public StripeService $stripeService,
        public PayPalService $paypalService,
        public XeroService $xeroService,
        public ReceiptService $receiptService
        // .... imagine 10 more services
    ) {}
    
    // imagine 10 functions, spread out across 1500 lines of code, none of which use all the dependencies

    public function getStripeCustomer(Customer $customer): StripeCustomer
    {
        return $this->stripeService->getCustomerByEmail($customer->email);
    }
}

When I call PaymentService@getStripeCustomer(), I am constructing all of the dependencies just to call one of them.

In an ideal world, this would be refactored into smaller components with fewer dependencies in each. That's not always a price a development team can pay all at once.

To simplify this, I am proposing introducing a #[Lazy] attribute, which can be applied to either a class or individual parameters.

class PaymentService
{
    public function __construct(
        #[Lazy] public CustomerService $customerService,
        #[Lazy] public StripeService $stripeService,
        // ...
    ) {}
}

Naming

Technically this is built using the proxy() function. I'm not sure that naming the attribute something other than Lazy is worth the distinction.

Other ideas

Adding a parameter bool $dependencies that would also make all of the dependencies lazy for the class

[cosmastech]

@timacdonald Would you mind taking a look at this when you have some time?

Not sure about the name... I guess technically the attribute should be #[Proxy] but I feel like that distinction is confusing.