First class callable syntax for instance methods

[rela589n]

Description

Consider the following code:

class Booking
{
    public function getFreeCancellationDeadline(): ?\DateTimeImmutable
    {
          //  ....
    }
}

Then, you'd like to have a closure:

fn (Booking $b): ?\DateTimeImmutable => $b->getFreeCancellationDeadline();

It would be much neater to have it like this:

Booking::getFreeCancellationDeadline(...);

This is the exact form in which PhpStorm IDE copies the method reference ("Copy Reference" on the method - Ctrl+Alt+Sft+C).

[TimWolla]

@arnaud-lb and I had already started working on this with https://news-web.php.net/php.internals/129846, but were planning to do a v2 based on Bob's feedback after PHP 8.6 lands.