Update the standard library to use the new `NonNull::without_provenance`

[scottmcm]

The function is new, cc #135243

But there's a bunch of places in the code that can be simplified now that it exists. A couple I found quickly:

library/alloc\src\rc.rs
3032:                NonNull::new_unchecked(ptr::without_provenance_mut::<RcInner<T>>(usize::MAX))
3059:                NonNull::new_unchecked(ptr::without_provenance_mut::<RcInner<T>>(usize::MAX))

library/alloc\src\sync.rs
2692:                NonNull::new_unchecked(ptr::without_provenance_mut::<ArcInner<T>>(usize::MAX))
2722:                NonNull::new_unchecked(ptr::without_provenance_mut::<ArcInner<T>>(usize::MAX))

library/core\src\alloc\layout.rs
237:        unsafe { NonNull::new_unchecked(crate::ptr::without_provenance_mut::<u8>(self.align())) }

library/std\src\io\error\repr_bitpacked.rs
179:            unsafe { NonNull::new_unchecked(ptr::without_provenance_mut(utagged)) },
196:            unsafe { NonNull::new_unchecked(ptr::without_provenance_mut(utagged)) },

It would be nice to simplify those like

-                NonNull::new_unchecked(ptr::without_provenance_mut::<RcInner<T>>(usize::MAX))
+                NonNull::without_provenance::<RcInner<T>>(NonZeroUsize::MAX)

and

-        unsafe { NonNull::new_unchecked(crate::ptr::without_provenance_mut::<u8>(self.align())) }
+        NonNull::without_provenance::<u8>(self.alignment.as_nonzero())

(or whatever it would be) to have shorter code that needs to prove fewer soundness preconditions.

[cod10129]

I can do this, it's just a matter of finding the places where this function would be useful. (I would find most of those with a grep for without_provenance_mut, right?). If there are more relevant cases that wouldn't be really hard to find then please tell me.

@rustbot claim

[samueltardieu]

@cod10129 In case you haven't done it yet, I have a PR ready already, I was waiting for the complete test results. If you want do to it anyway you can get inspiration from samueltardieu@9ab77f1 that I was about to submit.

[cod10129]

Never mind then. Go ahead and submit yours @samueltardieu

@rustbot release-assignment

[samueltardieu]

@rustbot claim