LibJS+LibWeb: Replace GlobalObject with Realm in object constructors

No functional changes - we can still very easily get to the global
object via `Realm::global_object()`. This is in preparation of moving
the intrinsics to the realm and no longer having to pass a global
object when allocating any object.
In a few (now, and many more in subsequent commits) places we get a
realm using `GlobalObject::associated_realm()`, this is intended to be
temporary. For example, create() functions will later receive the same
treatment and are passed a realm instead of a global object.

Userland/Libraries/LibJS/Runtime/AsyncGeneratorFunctionConstructor.h

@@ -14,7 +14,7 @@ class AsyncGeneratorFunctionConstructor final : public NativeFunction {
     JS_OBJECT(AsyncGeneratorFunctionConstructor, NativeFunction);
 
 public:
-    explicit AsyncGeneratorFunctionConstructor(GlobalObject&);
+    explicit AsyncGeneratorFunctionConstructor(Realm&);
     virtual void initialize(GlobalObject&) override;
     virtual ~AsyncGeneratorFunctionConstructor() override = default;