Change entry point to 🛡️ against 💥 💥-payloads

Guard against panic payloads panicking within entrypoints, where it is
UB to do so.

Note that there are a number of implementation approaches to consider.
Some simpler, some more complicated. This particular solution is nice in
that it also guards against accidental implementation issues in
various pieces of runtime code, something we cannot prevent statically
right now.

Fixes #86030

library/std/src/lib.rs

@@ -225,13 +225,14 @@
 #![feature(allocator_internals)]
 #![feature(allow_internal_unsafe)]
 #![feature(allow_internal_unstable)]
-#![feature(async_stream)]
 #![feature(arbitrary_self_types)]
 #![feature(array_error_internals)]
 #![feature(asm)]
 #![feature(assert_matches)]
 #![feature(associated_type_bounds)]
+#![feature(async_stream)]
 #![feature(atomic_mut_ptr)]
+#![feature(auto_traits)]
 #![feature(bench_black_box)]
 #![feature(box_syntax)]
 #![feature(c_variadic)]
@@ -244,14 +245,14 @@
 #![feature(concat_idents)]
 #![feature(const_cstr_unchecked)]
 #![feature(const_fn_floating_point_arithmetic)]
-#![feature(const_fn_transmute)]
 #![feature(const_fn_fn_ptr_basics)]
+#![feature(const_fn_transmute)]
 #![feature(const_io_structs)]
 #![feature(const_ip)]
+#![feature(const_ipv4)]
 #![feature(const_ipv6)]
 #![feature(const_raw_ptr_deref)]
 #![feature(const_socketaddr)]
-#![feature(const_ipv4)]
 #![feature(container_error_extra)]
 #![feature(core_intrinsics)]
 #![feature(custom_test_frameworks)]
@@ -297,7 +298,6 @@
 #![feature(nll)]
 #![feature(nonnull_slice_from_raw_parts)]
 #![feature(once_cell)]
-#![feature(auto_traits)]
 #![feature(panic_info_message)]
 #![feature(panic_internals)]
 #![feature(panic_unwind)]
@@ -330,6 +330,7 @@
 #![feature(unboxed_closures)]
 #![feature(unsafe_cell_raw_get)]
 #![feature(unwind_attributes)]
+#![feature(unwrap_infallible)]
 #![feature(vec_into_raw_parts)]
 #![feature(vec_spare_capacity)]
 // NB: the above list is sorted to minimize merge conflicts.