Stabilize `const_ptr_offset_from`.

Stabilization has been completed [here](https://github.com/rust-lang/rust/issues/92980#issuecomment-1065644848)
with a FCP.

library/core/src/intrinsics.rs

@@ -2013,11 +2013,11 @@ extern "rust-intrinsic" {
     pub fn nontemporal_store<T>(ptr: *mut T, val: T);
 
     /// See documentation of `<*const T>::offset_from` for details.
-    #[rustc_const_unstable(feature = "const_ptr_offset_from", issue = "92980")]
+    #[rustc_const_stable(feature = "const_ptr_offset_from", since = "1.65.0")]
     pub fn ptr_offset_from<T>(ptr: *const T, base: *const T) -> isize;
 
     /// See documentation of `<*const T>::sub_ptr` for details.
-    #[rustc_const_unstable(feature = "const_ptr_offset_from", issue = "92980")]
+    #[rustc_const_stable(feature = "const_ptr_offset_from", since = "1.65.0")]
     pub fn ptr_offset_from_unsigned<T>(ptr: *const T, base: *const T) -> usize;
 
     /// See documentation of `<*const T>::guaranteed_eq` for details.

library/core/src/lib.rs

@@ -130,7 +130,6 @@
 #![feature(const_replace)]
 #![feature(const_ptr_as_ref)]
 #![feature(const_ptr_is_null)]
-#![feature(const_ptr_offset_from)]
 #![feature(const_ptr_read)]
 #![feature(const_ptr_write)]
 #![feature(const_raw_ptr_comparison)]

library/core/src/ptr/const_ptr.rs

@@ -641,7 +641,7 @@ impl<T: ?Sized> *const T {
     /// }
     /// ```
     #[stable(feature = "ptr_offset_from", since = "1.47.0")]
-    #[rustc_const_unstable(feature = "const_ptr_offset_from", issue = "92980")]
+    #[rustc_const_stable(feature = "const_ptr_offset_from", since = "1.65.0")]
     #[inline]
     #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     pub const unsafe fn offset_from(self, origin: *const T) -> isize

library/core/src/ptr/mut_ptr.rs

@@ -824,7 +824,7 @@ impl<T: ?Sized> *mut T {
     /// }
     /// ```
     #[stable(feature = "ptr_offset_from", since = "1.47.0")]
-    #[rustc_const_unstable(feature = "const_ptr_offset_from", issue = "92980")]
+    #[rustc_const_stable(feature = "const_ptr_offset_from", since = "1.65.0")]
     #[inline(always)]
     #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     pub const unsafe fn offset_from(self, origin: *const T) -> isize

src/test/ui/consts/const-eval/issue-91827-extern-types.rs

@@ -3,7 +3,6 @@
 // Test that we can handle unsized types with an extern type tail part.
 // Regression test for issue #91827.
 
-#![feature(const_ptr_offset_from)]
 #![feature(extern_types)]
 
 use std::ptr::addr_of;

src/test/ui/consts/offset.rs

@@ -1,5 +1,4 @@
 // run-pass
-#![feature(const_ptr_offset_from)]
 use std::ptr;
 
 #[repr(C)]

src/test/ui/consts/offset_from.rs

@@ -1,6 +1,5 @@
 // run-pass
 
-#![feature(const_ptr_offset_from)]
 #![feature(const_ptr_sub_ptr)]
 #![feature(ptr_sub_ptr)]
 

src/test/ui/consts/offset_from_ub.rs

@@ -1,4 +1,3 @@
-#![feature(const_ptr_offset_from)]
 #![feature(core_intrinsics)]
 
 use std::intrinsics::{ptr_offset_from, ptr_offset_from_unsigned};