Qt provides a context where the depth test is disabled by default.
In general, vtkRenderer will take care of enabling the dept test in its
Clear() method at the beguining of the render call, but there are use
cases where the depth test is expected to be enabled before VTK renders:
1. If vtkRenderer::EraseOff() was called, Clear() won't be called and the
   depth test is left disabled
2. Render passes that restores the depth test initial value (e.g.
   vtkSSAOPass) will restore a disabled depth test for additional overlay
   renderers that could use EraseOff to prevent useless clearing.

Fixes [Slicer/Slicer#7518](https://github.com/Slicer/Slicer/issues/7518)

Co-authored by: @lassoan