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.h

@@ -20,7 +20,7 @@ class WEB_API ObservableArray final : public JS::Array {
 public:
     static GC::Ref<ObservableArray> create(JS::Realm& realm);
 
-    virtual JS::ThrowCompletionOr<bool> internal_set(JS::PropertyKey const& property_key, JS::Value value, JS::Value receiver, JS::CacheablePropertyMetadata* metadata = nullptr, PropertyLookupPhase = PropertyLookupPhase::OwnProperty) override;
+    virtual JS::ThrowCompletionOr<bool> internal_set(JS::PropertyKey const& property_key, JS::Value value, JS::Value receiver, JS::CacheableSetPropertyMetadata* metadata = nullptr, PropertyLookupPhase = PropertyLookupPhase::OwnProperty) override;
     virtual JS::ThrowCompletionOr<bool> internal_delete(JS::PropertyKey const& property_key) override;
 
     using SetAnIndexedValueCallbackFunction = Function<ExceptionOr<void>(JS::Value&)>;