Added overrides for the methods that take a vtkAbstractArray and dispatch
it, so that the common case of using these methods with NewInstance() can
avoid the dispatch overhead.

Also moved to vtkDataArrayRoundIfNecessary helpers from vtkDataArray.cxx
to vtkMath::RoundDoubleToIntegralIfNecessary so they can be reused from
other array implementations.

Also replaced some vtkDataArray::SafeDownCasts with FastDownCasts and
added more detail to some error messages.