A *lot* of import fixes for flatpak (#3909)

* A *lot* of import fixes for flatpak

Aside, thank you @hadess for the majority of these fixes. You are the
base point for a lot of issues fixed during the creation of this
flatpak.

* Use slic3r::load_string_file

Boost 1.84 removed `boost::fs::load_string_file` so use the func located
in Utils.hpp

src/slic3r/GUI/MediaPlayCtrl.cpp

@@ -8,6 +8,9 @@
 #include "MsgDialog.hpp"
 #include "DownloadProgressDialog.hpp"
 
+#include <boost/lexical_cast.hpp>
+#include <boost/log/trivial.hpp>
+#include <boost/nowide/cstdio.hpp>
 #include <boost/nowide/utf8_codecvt.hpp>
 #undef pid_t
 #include <boost/process.hpp>
@@ -18,6 +21,8 @@
 #include <sys/shm.h>
 #endif
 
+#include <wx/clipbrd.h>
+
 namespace Slic3r {
 namespace GUI {