HTG: add testing for new threshold modes

Filters/HyperTree/Testing/Cxx/CMakeLists.txt

...ee/Testing/Cxx/TestHyperTreeGridBinary2DThresholdDeep.cxx

...esting/Cxx/TestHyperTreeGridBinary2DThresholdImplicit.cxx

...ng/Cxx/TestHyperTreeGridBinary2DThresholdMaterialDeep.cxx

...xx/TestHyperTreeGridBinary2DThresholdMaterialImplicit.cxx

...e/Testing/Cxx/TestHyperTreeGridTernary3DThresholdDeep.cxx

...sting/Cxx/TestHyperTreeGridTernary3DThresholdImplicit.cxx

...g/Cxx/TestHyperTreeGridTernary3DThresholdMaterialDeep.cxx

...x/TestHyperTreeGridTernary3DThresholdMaterialImplicit.cxx

...aseline/TestHyperTreeGridBinary2DThresholdDeep.png.sha512

...ine/TestHyperTreeGridBinary2DThresholdImplicit.png.sha512

...TestHyperTreeGridBinary2DThresholdMaterialDeep.png.sha512

...HyperTreeGridBinary2DThresholdMaterialImplicit.png.sha512

...seline/TestHyperTreeGridTernary3DThresholdDeep.png.sha512

...ne/TestHyperTreeGridTernary3DThresholdImplicit.png.sha512

...estHyperTreeGridTernary3DThresholdMaterialDeep.png.sha512

...yperTreeGridTernary3DThresholdMaterialImplicit.png.sha512