LibJS: Add preparation for Temporal constructors and prototypes

Add a JS_ENUMERATE_TEMPORAL_OBJECTS macro and use it to generate:

- Forward declarations
- CommonPropertyNames class name members
- Constructor and prototype GlobalObject members, getters, visitors,
  and initialize_constructor() calls

Userland/Libraries/LibJS/Forward.h

@@ -76,6 +76,8 @@
     __JS_ENUMERATE(Float32Array, float32_array, Float32ArrayPrototype, Float32ArrayConstructor, float)                          \
     __JS_ENUMERATE(Float64Array, float64_array, Float64ArrayPrototype, Float64ArrayConstructor, double)
 
+#define JS_ENUMERATE_TEMPORAL_OBJECTS
+
 #define JS_ENUMERATE_ITERATOR_PROTOTYPES          \
     __JS_ENUMERATE(Iterator, iterator)            \
     __JS_ENUMERATE(ArrayIterator, array_iterator) \
@@ -185,6 +187,15 @@ JS_ENUMERATE_NATIVE_ERRORS
 JS_ENUMERATE_TYPED_ARRAYS
 #undef __JS_ENUMERATE
 
+namespace Temporal {
+#define __JS_ENUMERATE(ClassName, snake_name, ConstructorName, PrototypeName) \
+    class ClassName;                                                          \
+    class ConstructorName;                                                    \
+    class PrototypeName;
+JS_ENUMERATE_TEMPORAL_OBJECTS
+#undef __JS_ENUMERATE
+};
+
 template<class T>
 class Handle;