P1413R3: Deprecate `std::aligned_storage` and `std::aligned_union`

[ldionne]

Link: https://wg21.link/P1413R3

BEGIN-RST-NOTES
``std::aligned_storage_t`` and ``std::aligned_union_t`` are marked deprecated, but clang doesn't issue a diagnostic for deprecated using template declarations.
END-RST-NOTES

[ldionne]

This issue has already been implemented and was created for tracking purposes only.