Extract ArrayAccessRead from ArrayAccess

Hello, internals! Recently I was implementing some collections and realized that I cannot use ArrayAccess for immutable collections without throwing BadMethodCallException in offsetSet and offsetUnset. I also cannot have an interface ReadonlyCollection extends ArrayAccess, because offsetSet and offsetUnset are mutators and have TValue in a contravariant position. Here's the idea: let's extract ArrayAccess::offsetExists and ArrayAccess::offsetGet methods into a separate ArrayAccessRead interface (name can be different) and allow read operations `$exists = isset($object['key']) and $value = $object['key']` for objects of classes that implement this interface. ArrayAccess will then extend ArrayAccessRead and add the remaining 2 methods. Looks like this change should not break backward compatibility. ``` interface ArrayAccessRead { public function offsetExists(mixed $offset): bool; public function offsetGet(mixed $offset): mixed; } interface ArrayAccess extends ArrayAccessRead { public function offsetSet(mixed $offset, mixed $value): void; public function offsetUnset(mixed $offset): void; } // then interfaces of the doctrine/collections package might look like this: namespace Doctrine\Common\Collections; interface ReadableCollection extends Countable, IteratorAggregate, ArrayAccessRead {} interface Collection extends ReadableCollection, ArrayAccess {} ``` -- Regards, Valentin Udaltsov