Range-based for loops for vtkCollection; deprecation of vtkCollectionIterator

vtkCollection now supports C++11 range-based for loops, leveraging modern C++ syntax.

This, along with vtk::Range, should be preferred over using vtkCollectionIterator and vtkCollectionSimpleIterator and they are now deprecated.

Here’s a typical example of the old way:

vtkCollectionIterator* iter = this->AnimationCuesIterator;
for (iter->InitTraversal(); !iter->IsDoneWithTraversal(); iter->GoToNextItem())
{
  vtkAnimationCue* cue = vtkAnimationCue::SafeDownCast(iter->GetCurrentObject());

transformed:

for (vtkObject* obj : *(this->AnimationCues))
{
  vtkAnimationCue* cue = vtkAnimationCue::SafeDownCast(obj);

Note that since vtkCollection uses vtkObject (as opposed to being templated), the range-based for loops also use vtkObject and may require casting (as in both the old and new ways above).

All of VTK’s own uses have been updated. The only slight backwards incompatible change is that the protected member vtkCollectionIterator* AnimationCuesIterator in vtkAnimationScene has been removed. This may cause compatibility issues for anyone subclassing this class.