Rollup merge of #146187 - clarfonthey:const-drop-in-place, r=oli-obk

Unstably constify `ptr::drop_in_place` and related methods

Tracking: rust-lang/rust#109342
Supercedes: rust-lang/rust#145725

Makes methods const:

* `core::ptr::drop_in_place`
* `core::mem::ManuallyDrop::drop`
* `core::mem::MaybeUninit::assume_init_drop`
* `<[core::mem::MaybeUninit<_>]>::assume_init_drop`
* `<*mut _>::drop_in_place`
* `core::ptr::NonNull::drop_in_place`

Author: matthiaskrgr

tests/fail/stacked_borrows/drop_in_place_retag.stderr

@@ -1,8 +1,10 @@
 error: Undefined Behavior: trying to retag from <TAG> for Unique permission at ALLOC[0x0], but that tag only grants SharedReadOnly permission for this location
   --> RUSTLIB/core/src/ptr/mod.rs:LL:CC
    |
-LL | pub unsafe fn drop_in_place<T: PointeeSized>(to_drop: *mut T) {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this error occurs as part of retag at ALLOC[0x0..0x1]
+LL | / pub const unsafe fn drop_in_place<T: PointeeSized>(to_drop: *mut T)
+LL | | where
+LL | |     T: [const] Destruct,
+   | |________________________^ this error occurs as part of retag at ALLOC[0x0..0x1]
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
    = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information

tests/fail/unaligned_pointers/drop_in_place.stderr

@@ -1,8 +1,10 @@
 error: Undefined Behavior: constructing invalid value: encountered an unaligned reference (required ALIGN byte alignment but found ALIGN)
   --> RUSTLIB/core/src/ptr/mod.rs:LL:CC
    |
-LL | pub unsafe fn drop_in_place<T: PointeeSized>(to_drop: *mut T) {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
+LL | / pub const unsafe fn drop_in_place<T: PointeeSized>(to_drop: *mut T)
+LL | | where
+LL | |     T: [const] Destruct,
+   | |________________________^ Undefined Behavior occurred here
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information