This release implements submdspan with customizations points as approved by ISO C++ LEWG. It also reworks the implementation of extents, to reduce code complexity and improve compile time.

What's Changed

• Fix equality operator of layout_stride, after #196 by @youyu3 in https://github.com/kokkos/mdspan/pull/228
• Address issue #229 and fix missing noexcept by @crtrott in https://github.com/kokkos/mdspan/pull/230
• New submdspan implementation with customization point @crtrott in https://github.com/kokkos/mdspan/pull/227
• Update strided_index_range to strided_slice by @crtrott in https://github.com/kokkos/mdspan/pull/231
• Fix mdspan working with HIP by @crtrott in https://github.com/kokkos/mdspan/pull/233
• Enable testing with SYCL by @masterleinad in https://github.com/kokkos/mdspan/pull/234
• Fix return type of layout_stride operator, and add test by @crtrott in https://github.com/kokkos/mdspan/pull/236
• Add mdarray_to_mdspan by @crtrott in https://github.com/kokkos/mdspan/pull/240
• Bugfix: MSVC /Zc:preprocessor by @MattEding in https://github.com/kokkos/mdspan/pull/241
• Remove special gcc check by @adah1972 in https://github.com/kokkos/mdspan/pull/242