Tensor<rank,dim,Number> is now constexpr

Tensor<rank,dim,Number> is now constexpr

CONSEXPR macro added to Tensor<rank,dim,Number> functions. New constructors added to VectorizedArray<Number>

Tensor free functions all made constexpr

constexpr added to tensor_accessors.h

default initialization for VectorizedArray<Number>

constexpr feature added to Tensor<rank,dim,Number> class

adding DEAL_II_ALWAYS_INLINE back to functions in tensor_accessors.h

Add assignement operator ans default constructor back

Apply suggestions from code review

Typos fixed

Co-Authored-By: Daniel Arndt <arndtd@ornl.gov>
Indentation

Improve check_01_cxx_features.cmake

Fix changelog entry

static constexpr converted to back static const for VectorizedArray

one more constexpr tensor test

test failure fixed

added DEAL_II_CONSTEXPR to three more functions

removed member initialization in VectorizedArray

Avoid warning

constructor added to VectorizedArray<Number>

reverted the changes in vectorization.h

asserting VectorizedArray is POD