To manage ractor-local data for C extension, the following APIs
are defined.

* rb_ractor_local_storage_value_newkey
* rb_ractor_local_storage_value
* rb_ractor_local_storage_value_set
* rb_ractor_local_storage_ptr_newkey
* rb_ractor_local_storage_ptr
* rb_ractor_local_storage_ptr_set

At first, you need to create a key of storage by
rb_ractor_local_(value|ptr)_newkey().
For ptr storage, it accepts the type of storage,
how to mark and how to free with ractor's lifetime.

rb_ractor_local_storage_value/set are used to access a VALUE
and rb_ractor_local_storage_ptr/set are used to access a pointer.

random.c uses this API.