[feature-request] CTAD for `mdspan` from `mdarray`

it would be groovy if i could create an mdspan from an mdarray like mdspan{array}. something like this might work:

//! \brief Deduction guide for \c ::std::mdspan that makes its template parameters
//! deducable from a \c ::std::experimental::mdarray.
template <class ElementType, class Extents, class LayoutPolicy, class Container>
mdspan(experimental::mdarray<ElementType, Extents, LayoutPolicy, Container>&)
  -> mdspan<ElementType, Extents, LayoutPolicy>;

//! \overload
template <class ElementType, class Extents, class LayoutPolicy, class Container>
mdspan(const experimental::mdarray<ElementType, Extents, LayoutPolicy, Container>&)
  -> mdspan<const ElementType, Extents, LayoutPolicy>;

Start by locating the mdspan deduction guides and the mdarray definition in the repository. Check how mutable and const mdarray objects should deduce their mdspan element types, then add coverage for both forms and confirm the proposed mdspan{array} syntax compiles.