Auto merge of #123550 - GnomedDev:remove-initial-arc, r=Noratrieb

Remove the `Arc` rt::init allocation for thread info

Removes an allocation pre-main by just not storing anything in std:🧵: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.

tests/debuginfo/thread.rs

@@ -12,15 +12,15 @@
 // cdb-check:join_handle,d    [Type: std::thread::JoinHandle<tuple$<> >]
 // cdb-check:    [...] __0              [Type: std::thread::JoinInner<tuple$<> >]
 //
-// cdb-command:dx t,d
+// cdb-command:dx -r3 t,d
 // cdb-check:t,d              : [...] [Type: std::thread::Thread *]
-// cdb-check:[...] inner [...][Type: core::pin::Pin<alloc::sync::Arc<std::thread::Inner,alloc::alloc::Global> >]
+// cdb-check:    [...] __0              : Other [Type: enum2$<std::thread::Inner>]
+// cdb-check:         [...] __0              [Type: core::pin::Pin<alloc::sync::Arc<std::thread::OtherInner,[...]> >]
 
 use std::thread;
 
 #[allow(unused_variables)]
-fn main()
-{
+fn main() {
     let join_handle = thread::spawn(|| {
         println!("Initialize a thread");
     });