Move roughness from LayerInterface to Layer (#20)

Mikhail Svechnikovrequested to merge
m.i20 into main

MR does the first point of https://jugit.fz-juelich.de/mlz/intern/ba-intern/-/blob/main/internal_reports/2012_Polylayer.md:

Associate surface properties with `Layer`.

Class LayerInterface and API function AddLayerWithTopRoughness were deleted.

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