Remove the `Arc` rt::init allocation for thread info Removes an allocation pre-main by just not storing anything in std::thread::Thread for the main thread. - The thread name can just be a hard coded literal, as was done in #123433. - Storing ThreadId and Parker in a static that is initialized once at startup. This uses SyncUnsafeCell and MaybeUninit as this is quite performance critical and we don't need synchronization or to store a tag value and possibly leave in a panic.