QVTKOpenGLWidget fixes

Adding some fixes for QVTKOpenGLWidget:

• Add method to set the cursor so the cursor issue detected by @utkarsh.ayachit can be adressed in ParaView
• Unify QVTKOpenGLWidget and QVTKOpenGLSimpleWidget api
• Fix TestQVTKOpenGLSimpleWidgetWithDisableInteractor
• Add a work around at QVTKOpenGLSimpleWidget level for paraview/paraview#18213 (closed)
• Fix paraview/paraview#18285 (closed) where the whole paraview window could be dragged
• Fix an issue related to glViewport detected by !4523 (merged) (closes paraview/paraview#18346 (closed))