Implement first class callable syntax for instance method references

[thekid]

Inspired by https://externals.io/message/120011

class Person {
  public function __construct(private string $name) { }
  public function name(): string { return $this->name; }
}

$group= [new Person('Timm'), new Person('Alex')];

// Instead of the following:
$names= array_map(fn($person) => $person->name(), $group);

// ...we can now write this:
$names= array_map(Person->name(...), $group);

// ["Timm", "Alex"]