Rollup merge of rust-lang#97524 - ibraheemdev:thread-raw, r=joshtriplett

Add `Thread::{into_raw, from_raw}`

Public API:
```rust
#![unstable(feature = "thread_raw", issue = "97523")]

impl Thread {
    pub fn into_raw(self) -> *const ();
    pub unsafe fn from_raw(ptr: *const ()) -> Thread;
}
```

ACP: rust-lang/libs-team#200

library/std/src/thread/mod.rs

@@ -1503,6 +1503,52 @@ impl Thread {
         self.inner.name.as_str()
     }
 
+    /// Consumes the `Thread`, returning a raw pointer.
+    ///
+    /// To avoid a memory leak the pointer must be converted
+    /// back into a `Thread` using [`Thread::from_raw`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(thread_raw)]
+    ///
+    /// use std::thread::{self, Thread};
+    ///
+    /// let thread = thread::current();
+    /// let id = thread.id();
+    /// let ptr = Thread::into_raw(thread);
+    /// unsafe {
+    ///     assert_eq!(Thread::from_raw(ptr).id(), id);
+    /// }
+    /// ```
+    #[unstable(feature = "thread_raw", issue = "97523")]
+    pub fn into_raw(self) -> *const () {
+        Arc::into_raw(Pin::into_inner(self.inner)) as *const ()
+    }
+
+    /// Constructs a `Thread` from a raw pointer.
+    ///
+    /// The raw pointer must have been previously returned
+    /// by a call to [`Thread::into_raw`].
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because improper use may lead
+    /// to memory unsafety, even if the returned `Thread` is never
+    /// accessed.
+    ///
+    /// Creating a `Thread` from a pointer other than one returned
+    /// from [`Thread::into_raw`] is **undefined behavior**.
+    ///
+    /// Calling this function twice on the same raw pointer can lead
+    /// to a double-free if both `Thread` instances are dropped.
+    #[unstable(feature = "thread_raw", issue = "97523")]
+    pub unsafe fn from_raw(ptr: *const ()) -> Thread {
+        // SAFETY: upheld by caller
+        unsafe { Thread { inner: Pin::new_unchecked(Arc::from_raw(ptr as *const Inner)) } }
+    }
+
     fn cname(&self) -> Option<&CStr> {
         self.inner.name.as_cstr()
     }