Rollup merge of rust-lang#86726 - sexxi-goose:use-diagnostic-item-for-rfc2229-migration, r=nikomatsakis

Use diagnostic items instead of lang items for rfc2229 migrations

This PR removes the `Send`, `UnwindSafe` and `RefUnwindSafe` lang items introduced in rust-lang#84730, and uses diagnostic items instead to check for `Send`, `UnwindSafe` and `RefUnwindSafe` traits for RFC2229 migrations.

r? ```@nikomatsakis```

Author: GuillaumeGomez

core/src/marker.rs

@@ -31,7 +31,6 @@ use crate::hash::Hasher;
 /// [ub]: ../../reference/behavior-considered-undefined.html
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "send_trait")]
-#[lang = "send"]
 #[rustc_on_unimplemented(
     message = "`{Self}` cannot be sent between threads safely",
     label = "`{Self}` cannot be sent between threads safely"

std/src/panic.rs

@@ -133,7 +133,7 @@ pub fn panic_any<M: 'static + Any + Send>(msg: M) -> ! {
 /// [`AssertUnwindSafe`] wrapper struct can be used to force this trait to be
 /// implemented for any closed over variables passed to `catch_unwind`.
 #[stable(feature = "catch_unwind", since = "1.9.0")]
-#[cfg_attr(not(test), lang = "unwind_safe")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "unwind_safe_trait")]
 #[rustc_on_unimplemented(
     message = "the type `{Self}` may not be safely transferred across an unwind boundary",
     label = "`{Self}` may not be safely transferred across an unwind boundary"
@@ -149,7 +149,7 @@ pub auto trait UnwindSafe {}
 /// This is a "helper marker trait" used to provide impl blocks for the
 /// [`UnwindSafe`] trait, for more information see that documentation.
 #[stable(feature = "catch_unwind", since = "1.9.0")]
-#[cfg_attr(not(test), lang = "ref_unwind_safe")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "ref_unwind_safe_trait")]
 #[rustc_on_unimplemented(
     message = "the type `{Self}` may contain interior mutability and a reference may not be safely \
                transferrable across a catch_unwind boundary",