Enable human readable sizes for vtkm::Id

The functions GetHumanReadableSize and GetSizeString accepted a vtkm::UInt64 as the size, which should hold pretty much any reasonable memory size and is compatible with std::size_t. But it has a different sign-ness as vtkm::Id. So if you are holding an array size with vtkm::Id (which is common), you could get a compiler warning when using these functions, which is annoying. So, for convenience add a second form of these methods that takes a vtkm::Id and automatically converts.