Confusing wording in docs for slice::as_ptr/as_mut_ptr

[crumblingstatue]

Modifying the slice may cause its buffer to be reallocated, which would also make any pointers to it invalid.

I believe this is trying to refer to manipulating the data structure (e.g. Vec) that owns the memory the slice is borrowing, but modifying the slice data through a slice can never cause reallocation.

[QuietMisdreavus]

I opened #40603 to tweak this wording.