Auto merge of #80851 - m-ou-se:panic-2021, r=petrochenkov

Implement Rust 2021 panic

This implements the Rust 2021 versions of `panic!()`. See https://github.com/rust-lang/rust/issues/80162 and https://github.com/rust-lang/rfcs/pull/3007.

It does so by replacing `{std, core}::panic!()` by a bulitin macro that expands to either `$crate::panic::panic_2015!(..)` or `$crate::panic::panic_2021!(..)` depending on the edition of the caller.

This does not yet make std's panic an alias for core's panic on Rust 2021 as the RFC proposes. That will be a separate change: https://github.com/rust-lang/rust/pull/80879/commits/c5273bdfb266c35e8eab9413aa8d58d27fdbe114 That change is blocked on figuring out what to do with https://github.com/rust-lang/rust/issues/80846 first.

compiler/rustc_span/src/symbol.rs

@@ -398,6 +398,8 @@ symbols! {
         copysignf64,
         core,
         core_intrinsics,
+        core_panic,
+        core_panic_2015_macro,
         core_panic_macro,
         cosf32,
         cosf64,
@@ -795,6 +797,8 @@ symbols! {
         owned_box,
         packed,
         panic,
+        panic_2015,
+        panic_2021,
         panic_abort,
         panic_bounds_check,
         panic_handler,
@@ -1096,6 +1100,8 @@ symbols! {
         staticlib,
         std,
         std_inject,
+        std_panic,
+        std_panic_2015_macro,
         std_panic_macro,
         stmt,
         stmt_expr_attributes,