vtkSynchronizedTemplates2D relies only on InputArrayToProcess

• the Scalars array was still used to get Increments (to navigate in the data array raw pointer) leading to some inconsitencies when Scalars has a different memory layout than the effective InputArrayToProcess

fix #19386 (closed)

Test was disabled due to ImageComparison (see #19221) Reimplement it in C++ to use CompareDataObjects instead of rendering.