mfem: mfem::Array rule of 5 methods don't check if typename T is plain old data

The mfem::Array<T> documentation states that typename T must be plain old data. As of C++11, this condition is testable via the <type_traits> header, e.g.:

#include <type_traits>
#include <iostream>

// std::is_pod<T> also works, but is deprecated as of C++20
if (std::is_trivial<T> && std::is_standard_layout<T>)
{
    std::cout << "Type is plain old data" << std::endl;
}
else
{
    std::cout << "Type is not plain old data" << std::endl;
}

A code snippet like this could be used to enforce the design contract declared in the documentation, assuming the project is amenable to the idea.