Rollup merge of #46287 - SimonSapin:stable-constness, r=aturon

Stabilize const-calling existing const-fns in std

Fixes #46038

src/test/ui/span/dropck_arr_cycle_checked.rs

@@ -13,7 +13,7 @@
 //
 // (Compare against compile-fail/dropck_vec_cycle_checked.rs)
 
-#![feature(const_atomic_usize_new)]
+
 
 use std::cell::Cell;
 use id::Id;

src/test/ui/span/dropck_vec_cycle_checked.rs

@@ -12,7 +12,7 @@
 //
 // (Compare against compile-fail/dropck_arr_cycle_checked.rs)
 
-#![feature(const_atomic_usize_new)]
+
 
 use std::cell::Cell;
 use id::Id;

src/test/ui/span/vec-must-not-hide-type-from-dropck.rs

@@ -23,7 +23,7 @@
 // conditions above to be satisfied, meaning that if the dropck is
 // sound, it should reject this code.
 
-#![feature(const_atomic_usize_new)]
+
 
 use std::cell::Cell;
 use id::Id;