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/GCodeWriter.hpp

@@ -2,8 +2,14 @@
 #define slic3r_GCodeWriter_hpp_
 
 #include "libslic3r.h"
+#include <cstddef>
+#include <cassert>
+#include <array>
+#include <cmath>
+#include <cstring>
 #include <string>
 #include <charconv>
+#include <vector>
 #include "Extruder.hpp"
 #include "Point.hpp"
 #include "Polygon.hpp"