Add Missing Includes Across src/slic3r/GUI

Every GUI 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, plus one hand edit making CalibrationPanel.hpp self-contained.

src/slic3r/GUI/Downloader.cpp

@@ -5,8 +5,22 @@
 #include "MainFrame.hpp"
 
 #include <boost/algorithm/string.hpp>
+#include <boost/filesystem/path.hpp>
 #include <boost/log/trivial.hpp>
 #include <boost/regex.hpp>
+#include <string>
+#include <wx/utils.h>
+#include <utility>
+#include <cstddef>
+#include <wx/event.h>
+#include <cassert>
+#include <memory>
+#include "slic3r/GUI/DownloaderFileGet.hpp"
+#include "libslic3r/Utils.hpp"
+#include <functional>
+#include "slic3r/GUI/GUI.hpp"
+#include "slic3r/GUI/Gizmos/GLGizmoBase.hpp"
+#include <wx/arrstr.h>
 
 namespace Slic3r {
 namespace GUI {