LibJS: Add inline caching for adding new own properties to objects

We already had IC support in PutById for the following cases:
- Changing an existing own property
- Calling a setter located in the prototype chain

This was enough to speed up code where structurally identical objects
(same shape) are processed in a loop:
```js
const arr = [{ a: 1 }, { a: 2 }, { a: 3 }];
for (let obj of arr) {
    obj.a += 1;
}
```

However, creating structurally identical objects in a loop was still
slow:
```js
for (let i = 0; i < 10_000_000; i++) {
    const o = {};
    o.a = 1;
    o.b = 2;
    o.c = 3;
}
```

This change addresses that by adding a new IC type that caches both the
source and target shapes, allowing property additions to be fast-pathed
by directly jumping to the shape that already includes the new property.

Libraries/LibWeb/WebIDL/ObservableArray.cpp

@@ -39,7 +39,7 @@ void ObservableArray::set_on_delete_an_indexed_value_callback(DeleteAnIndexedVal
     m_on_delete_an_indexed_value = GC::create_function(heap(), move(callback));
 }
 
-JS::ThrowCompletionOr<bool> ObservableArray::internal_set(JS::PropertyKey const& property_key, JS::Value value, JS::Value receiver, JS::CacheablePropertyMetadata* metadata, PropertyLookupPhase phase)
+JS::ThrowCompletionOr<bool> ObservableArray::internal_set(JS::PropertyKey const& property_key, JS::Value value, JS::Value receiver, JS::CacheableSetPropertyMetadata* metadata, PropertyLookupPhase phase)
 {
     if (property_key.is_number() && m_on_set_an_indexed_value)
         TRY(Bindings::throw_dom_exception_if_needed(vm(), [&] { return m_on_set_an_indexed_value->function()(value); }));