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/GCode/GCodeProcessor.cpp

@@ -1,14 +1,30 @@
+#include "libslic3r/Config.hpp"
+#include "libslic3r/CustomGCode.hpp"
+#include "libslic3r/Exception.hpp"
+#include "libslic3r/BoundingBox.hpp"
+#include "libslic3r/CommonDefs.hpp"
+#include "libslic3r/ArcFitter.hpp"
 #include "ExtrusionEntity.hpp"
+#include "libslic3r/GCodeReader.hpp"
 #include "GCodeWriter.hpp"
+#include "libslic3r/Point.hpp"
+#include "libslic3r/PrintBase.hpp"
+#include "libslic3r/Polygon.hpp"
 #include "PrintConfig.hpp"
+#include "libslic3r/TriangleSelector.hpp"
 #include "libslic3r/libslic3r.h"
 #include "libslic3r/Utils.hpp"
 #include "libslic3r/Print.hpp"
 #include "libslic3r/ClipperUtils.hpp"
 #include "libslic3r/LocalesUtils.hpp"
 #include "libslic3r/format.hpp"
+#include "libslic3r_version.h"
 #include "GCodeProcessor.hpp"
 
+#include <algorithm>
+#include <array>
+#include <boost/algorithm/string/classification.hpp>
+#include <boost/algorithm/string/constants.hpp>
 #include <boost/log/trivial.hpp>
 #include <boost/algorithm/string/predicate.hpp>
 #include <boost/algorithm/string/split.hpp>
@@ -16,15 +32,38 @@
 #include <boost/nowide/cstdio.hpp>
 #include <boost/filesystem/path.hpp>
 
+#include <cstddef>
+#include <cmath>
+#include <exception>
+#include <deque>
+#include <cstdio>
+#include <cstring>
+#include <cctype>
+#include <cstdlib>
+#include <climits>
 #include <fast_float/fast_float.h>
 
 #include <float.h>
 #include <assert.h>
+#include <memory>
+#include <optional>
+#include <iterator>
+#include <functional>
+#include <math.h>
+#include <map>
+#include <limits>
+#include <fstream>
 #include <regex>
+#include <set>
 #include <sstream>
 #include <charconv>
 #include <string>
+#include <string_view>
 #include <system_error>
+#include <vector>
+#include <type_traits>
+#include <unordered_map>
+#include <unordered_set>
 
 #if __has_include(<charconv>)
     #include <charconv>