Rollup merge of rust-lang#110049 - SkiFire13:localkey-with-docs-fix, r=workingjubilee

Don't claim `LocalKey::with` prevents a reference to be sent across threads

The documentation for `LocalKey` claims that `with` yields a reference that cannot be sent across threads, but this is false since you can easily do that with scoped threads. What it actually prevents is the reference from outliving the current thread.

Author: matthiaskrgr

library/std/src/thread/local.rs

@@ -18,8 +18,8 @@ use crate::fmt;
 /// target platform. It is instantiated with the [`thread_local!`] macro and the
 /// primary method is the [`with`] method.
 ///
-/// The [`with`] method yields a reference to the contained value which cannot be
-/// sent across threads or escape the given closure.
+/// The [`with`] method yields a reference to the contained value which cannot
+/// outlive the current thread or escape the given closure.
 ///
 /// [`thread_local!`]: crate::thread_local
 ///