Remove the Arc rt::init allocation for thread info

[GnomedDev]

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 Remove rt::init allocation for thread name #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.