ENH: Enable selection of translucent geometry

vtkHardwareSelector was skipping all translucent geometry and selecting only
opaque geometry. This change enables selection of translucent as well as opaque
geometry. Totally transparent (opacity = 0.0) is skipped.
This change fixes ParaView issue 14412

Change-Id: Ic8ead1534b4f24695e5138fc8207250f25450508