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.cpp

@@ -1,16 +1,36 @@
 #include "GCodeWriter.hpp"
+#include "Config.hpp"
 #include "CustomGCode.hpp"
+#include "Extruder.hpp"
 #include "I18N.hpp"
+#include "Point.hpp"
+#include "Polygon.hpp"
 #include "PrintConfig.hpp"
 #include "ClipperUtils.hpp"
 #include "Geometry/ArcWelder.hpp"
 #include "Line.hpp"
+#include "libslic3r.h"
 #include <algorithm>
+#include <cmath>
+#include <cstddef>
+#include <cstdlib>
+#include <array>
+#include <cstdint>
+#include <charconv>
+#include <cstring>
 #include <iomanip>
 #include <iostream>
+#include <iterator>
+#include <limits>
 #include <map>
 #include <assert.h>
 #include <GCode/GCodeProcessor.hpp>
+#include <string>
+#include <vector>
+#include <utility>
+#include <sstream>
+#include <stdexcept>
+#include <math.h>
 
 #ifdef __APPLE__
     #include <boost/spirit/include/karma.hpp>