`map_each_in_place` doesn't check or increase alignment

[joseph-isaacs]

See

    fn map_each_in_place_keeps_output_alignment_valid() {
        let bytes = BufferMut::<[u8; 4]>::copy_from_aligned([[1u8, 0, 0, 0]], Alignment::new(1));
        assert_eq!(1, Layout::new::<[u8; 4]>().align());
        let words = bytes.map_each_in_place(u32::from_ne_bytes);

        assert_eq!(words.as_slice(), [1]);
        assert!(words.alignment().is_aligned_to(Alignment::of::<u32>()));
    }
``