Rollup merge of #92030 - rukai:stdlib2021, r=m-ou-se

Update stdlib to the 2021 edition

progress towards https://github.com/rust-lang/rust/issues/88638

I couldnt find a way to run the 2018 style panic tests against 2018 so I just deleted them, maybe theres a way to do it that I missed though?

src/tools/tidy/src/edition.rs

@@ -23,8 +23,10 @@ pub fn check(path: &Path, bad: &mut bool) {
                 return;
             }
 
-            // Library crates are not yet ready to migrate to 2021.
-            if path.components().any(|c| c.as_os_str() == "library") {
+            // Not all library crates are ready to migrate to 2021.
+            if file.components().any(|c| c.as_os_str() == "library")
+                && file.components().all(|c| c.as_os_str() != "std")
+            {
                 let has = contents.lines().any(is_edition_2018);
                 if !has {
                     tidy_error!(