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/ElephantFootCompensation.cpp

@@ -1,3 +1,6 @@
+#include "Point.hpp"
+#include "BoundingBox.hpp"
+#include "Polygon.hpp"
 #include "clipper/clipper_z.hpp"
 
 #include "libslic3r.h"
@@ -10,8 +13,14 @@
 #include "SVG.hpp"
 #include "Utils.hpp"
 
+#include <algorithm>
 #include <cmath>
 #include <cassert>
+#include <cstddef>
+#include <vector>
+#include <utility>
+#include <math.h>
+#include <limits>
 
 // #define CONTOUR_DISTANCE_DEBUG_SVG