ENH: upgrade to use some C++17 constructs

- 'if constexpr (...)'
   * instead of std::enable_if
   * terminate template recursion
   * compile-time elimination of code

- use C++14 '_t', '_v' versions,
  eg, std::is_integral_v<T> instead of std::is_integral<T>::value

- std::begin, std::end, std::void_t instead of prev stdFoam versions

- provide is_contiguous_v<..> as short form of is_contiguous<..>::value
  with the additional benefit of removing any cv qualifiers.

ENH: include is_rotational_vectorspace trait

- tests for vector-space and nComponents > 1 (ie, not sphericalTensor)

ENH: improve robustness of pTraits_.. tests by removing cv qualifiers

applications/test/IOField/Test-IOField.cxx

@@ -213,11 +213,10 @@ int main(int argc, char *argv[])
             mesh
         );
 
-        Info<< "points path: " << io.typeFilePath<labelIOList>() << nl;
-        Info<< "points path: " << io.typeFilePath<void>() << nl;
+        Info<< "points path: " << io.typeFilePath<pointIOField>() << nl;
 
         io.resetHeader("bad-points");
-        Info<< "bad path: " << io.typeFilePath<void>() << nl;
+        Info<< "bad path: " << io.typeFilePath<labelIOList>() << nl;
     }
 
     IOobject io