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/SelectMachine.cpp

@@ -120,6 +120,9 @@
 #include "Notebook.hpp"
 #include "BitmapCache.hpp"
 #include "BindDialog.hpp"
+#include <boost/filesystem.hpp>
+
+namespace fs = boost::filesystem;
 
 namespace Slic3r { namespace GUI {