* sparse_set: stable virtual remove * basic_storage: fake get for empty types, * sigh_storage_mixin: use swap_and_pop, drop ::remove, ignore emptiness * poly_storage: ::remove is no longer part of its interface by default
* sparse_set: stable virtual remove * basic_storage: fake get for empty types, * sigh_storage_mixin: use swap_and_pop, drop ::remove, ignore emptiness * poly_storage: ::remove is no longer part of its interface by default