Merge pull request #15739 from bangerth/_v

[C++17] Use std::is_same_v instead of std::is_same<...>::value.

diff --cc include/deal.II/base/template_constraints.h
Simple merge

diff --cc include/deal.II/differentiation/ad/ad_number_traits.h
Simple merge

diff --cc include/deal.II/differentiation/ad/adolc_number_types.h
Simple merge