Added a multi files test using the test data of the multi files test as provided by Jeremey.Is also part of review for Issue [MWDAM-1666]Related to Issue [MWDAM-1673]
Refactored: move method SurfaceLine.CreateLoweredSurfaceLineForGivenLayerThickness() to a new class and method SurfacelineProcessor.CreateLoweredSurfaceLine()Related to Issue [MWDAM-1658]