Allow hooks in `readonly` promoted properties

Dear Internals, I am sending my first message here. Thank you all for your hard work! PHP has evolved amazingly over the past few years; I love it. Promoted properties allow us to write very neat value objects, with almost no boilerplate. Now, with property hooks, we can eliminate even more boilerplate. However, there is a bummer. When we want to use a set hook to add a simple mapper or validator, we are have to deal with asymmetric visibility, and refactor the whole class. Here in user land, I don't see a clear reason for that. Ideally, I would simply like to handle what will be set without having to deal with the general visibility of the class or its properties. Currently, instead of: ```php final readonly class Entry { public function __construct( public string $word, public string $slug, public string $file, public string $path, public array $lemmas { set(array $value) => array_map(static function (Lemma|array $lemma): Lemma { return $lemma instanceof Lemma ? $lemma : new Lemma(...$lemma); }, $value); }, ) {} } ``` we must refactor our entire class and will arrive at: ```php final class Entry // no more readonly { public function __construct( public readonly string $word, // added readonly public readonly string $slug, // added readonly public readonly string $file, // added readonly public readonly string $path, // added readonly private(set) array $lemmas { // added visibility set(array $value) => array_map(static function (Lemma|array $lemma): Lemma { return $lemma instanceof Lemma ? $lemma : new Lemma(...$lemma); }, $value); }, ) {} } ``` The downsides are: - the class can no longer be readonly - each property must be set to readonly - hooked properties must use private(set) There are many unrelated things we need to think about just to use a set hook. The example object is tiny and already then feels so much denser. Think of a bigger object if you like. For each added property, we once again must add the readonly keyword. Unnecessary noise, IMHO. Personally, this puts me off adopting property hooks -- because right now, a good old factory method is, subjectively, more clean/clear. I believe promoted properties should allowed for readonly properties and in readonly classes. This would help us to avoid the unnecessary boilerplate like outlined above. That said, I would greatly appreciate if internals could explore to allow readonly for hooks in promoted properties in 8.5. -- Cheers & thanks, Nick