Perform a batch copy in vtkPoints::GetPoints.

This avoids the overhead of copying each point individually.
Instead, let the container decide the best copy strategy.

Change-Id: Ia12904c19fef8fe897170ceb731c1203e4998f20
Speed up vtkUnstructuredGrid::GetCell implementation.

Use batch retrievals and std::copy where possible.

Change-Id: I712624c64b8c5901db0a97ba5acb525df17bd6a8
Merge topic 'ugrid-get-cell-performance-tweaks' into master

9cba78ad Speed up vtkUnstructuredGrid::GetCell implementation.
1183f7eb Perform a batch copy in vtkPoints::GetPoints.