hybrid-array: Convert &[[T; N]] to &[Array<T, N>]

[sinui0]

Noticed that yall are looking to migrate to hybrid-array instead of bumping to generic-array 1.0, thought I'd get ahead of this:

Can hybrid-array provide conversion methods to/from slices of core arrays?

Eg:

pub fn from_core_arrays_mut<const U: usize>(arrs: &mut [[T; U]]) -> &mut [Array<T, N>] {}

This helps support dependent code which already uses const generics.

Related: fizyk20/generic-array#145

[tarcieri]

Yes, we can support that