Add Missing Includes Across src/libslic3r

Every libslic3r source and header now directly includes the headers declaring what it uses, rather than relying on the precompiled header or transitive includes. Generated with clang-tidy misc-include-cleaner, with libslic3r headers spelled libslic3r/... so they resolve outside the library's private include paths. MultiMaterialSegmentation.hpp, Support/SupportParameters.hpp and Format/STEP.hpp are made self-contained by hand.

src/libslic3r/Arachne/utils/PolylineStitcher.cpp

@@ -4,6 +4,7 @@
 #include "PolylineStitcher.hpp"
 
 #include "ExtrusionLine.hpp"
+#include "libslic3r/Point.hpp"
 #include "libslic3r/Arachne/utils/PolygonsPointIndex.hpp"
 #include "libslic3r/Polygon.hpp"