Stop Format/STEP.hpp Defining a Global fs Alias (#16102)

Every file that included STEP.hpp, directly or not, got namespace fs = boost::filesystem at global scope, and 29 sources and three headers relied on it without saying so. Headers now spell out boost::filesystem, and each source that uses fs declares the alias itself.

src/slic3r/GUI/WipeTowerDialog.cpp

@@ -40,6 +40,9 @@
 #include "libslic3r/Config.hpp"
 #include "Widgets/Label.hpp"
 #include "MainFrame.hpp"
+#include <boost/filesystem.hpp>
+
+namespace fs = boost::filesystem;
 
 using namespace Slic3r;
 using namespace Slic3r::GUI;