Squash merge of lh_brim_rework,

brim separated to Brim.cpp,hpp
Refactored accessors to PrintObjectPtrs, PrintRegionPtrs, LayerPtrs,
SupportLayerPtrs for const correctness.

src/libslic3r/CMakeLists.txt

@@ -21,6 +21,8 @@ add_library(libslic3r STATIC
     BoundingBox.hpp
     BridgeDetector.cpp
     BridgeDetector.hpp
+    Brim.cpp
+    Brim.hpp
     ClipperUtils.cpp
     ClipperUtils.hpp
     Config.cpp