Auto merge of #33803 - WiSaGaN:feature/rename-main-thread, r=alexcrichton

Rename main thread from "<main>" to "main".

Fix issue #33789

We may need to discuss whether this counts as a breaking change since code may check the main thread name against "\<main\>". Discussion is in #33789

src/libstd/rt.rs

@@ -48,7 +48,7 @@ fn lang_start(main: *const u8, argc: isize, argv: *const *const u8) -> isize {
         // created. Note that this isn't necessary in general for new threads,
         // but we just do this to name the main thread and to give it correct
         // info about the stack bounds.
-        let thread: Thread = NewThread::new(Some("<main>".to_owned()));
+        let thread: Thread = NewThread::new(Some("main".to_owned()));
         thread_info::set(main_guard, thread);
 
         // Store our args if necessary in a squirreled away location