BUG #14602. Fixed text position not being saved in state files.

The bug was stemming from the fact the the property links set up in
vtkSMNewWidgetRepresentationProxy between the in/out properties was getting
destroyed prematurely due to incorrect logic to track reference counting.
The reference count tracking logic is indeed fragile. Instead, changed
vtkSMPropertyLink to not use vtkSmartPointer, instead use vtkWeakPointer. Then
vtkSMNewWidgetRepresentationProxy no longer needs to do anything special to
avoid leaks. With the link working again, state file correctly saves the values
for Position1 and Position2, thus overcoming the bug.

Change-Id: Icdeb9dbacd13d9c4f8fc48663624533b7f624b67
Merge topic '14602_fix_text_representation' into next

07694987 BUG #14602. Fixed text position not being saved in state files.