Rollup merge of rust-lang#148752 - nxsaken:const_manually_drop_take, r=scottmcm

Constify `ManuallyDrop::take`

Feature: `const_manually_drop_take`
Tracking issue: rust-lang#148773

This PR constifies `ManuallyDrop::take`.

Author: Zalathar

library/core/src/mem/manually_drop.rs

@@ -217,8 +217,9 @@ impl<T> ManuallyDrop<T> {
     ///
     #[must_use = "if you don't need the value, you can use `ManuallyDrop::drop` instead"]
     #[stable(feature = "manually_drop_take", since = "1.42.0")]
+    #[rustc_const_unstable(feature = "const_manually_drop_take", issue = "148773")]
     #[inline]
-    pub unsafe fn take(slot: &mut ManuallyDrop<T>) -> T {
+    pub const unsafe fn take(slot: &mut ManuallyDrop<T>) -> T {
         // SAFETY: we are reading from a reference, which is guaranteed
         // to be valid for reads.
         unsafe { ptr::read(&slot.value) }