Rollup merge of #133987 - Will-Low:DefineTlsAcronym, r=workingjubilee

Define acronym for thread local storage

There are multiple references in this module's documentation to the acronym "TLS" (meaning "thread local storage"), without defining it. This is confusing for the reader.

I propose that this acronym be defined during the first use of the term.

library/std/src/thread/local.rs

@@ -12,7 +12,7 @@ use crate::cell::{Cell, RefCell};
 use crate::error::Error;
 use crate::fmt;
 
-/// A thread local storage key which owns its contents.
+/// A thread local storage (TLS) key which owns its contents.
 ///
 /// This key uses the fastest possible implementation available to it for the
 /// target platform. It is instantiated with the [`thread_local!`] macro and the