Rollup merge of #74450 - aticu:master, r=jonas-schievink
Rollup merge of #74450 - aticu:master, r=jonas-schievink

Fix `Safety` docs for `from_raw_parts_mut`

This aligns the wording more with the documentation of e.g. `drop_in_place`, `replace`, `swap` and `swap_nonoverlapping` from `core::ptr`.

Also if the pointer were really only valid for writes, it would be trivial to introduce UB from safe code, after calling `core::slice::from_raw_parts_mut`.

graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust