Rollup merge of #76665 - RalfJung:slice-from-raw, r=sfackler

slice::from_raw_parts: explicitly mention that data must be initialized

This reflects the status quo, until the discussion in rust-lang/unsafe-code-guidelines#77 reaches a conclusion.

library/core/src/slice/mod.rs

@@ -6680,6 +6680,8 @@ unsafe impl<'a, T> TrustedRandomAccess for RChunksExactMut<'a, T> {
 ///       them from other data. You can obtain a pointer that is usable as `data`
 ///       for zero-length slices using [`NonNull::dangling()`].
 ///
+/// * `data` must point to `len` consecutive properly initialized values of type `T`.
+///
 /// * The memory referenced by the returned slice must not be mutated for the duration
 ///   of lifetime `'a`, except inside an `UnsafeCell`.
 ///
@@ -6767,6 +6769,8 @@ pub unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T] {
 ///       them from other data. You can obtain a pointer that is usable as `data`
 ///       for zero-length slices using [`NonNull::dangling()`].
 ///
+/// * `data` must point to `len` consecutive properly initialized values of type `T`.
+///
 /// * The memory referenced by the returned slice must not be accessed through any other pointer
 ///   (not derived from the return value) for the duration of lifetime `'a`.
 ///   Both read and write accesses are forbidden.