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/PrivacyUpdateDialog.cpp

@@ -21,6 +21,9 @@
 #include <wx/log.h>
 #include <wx/webview.h>
 #include <wx/utils.h>
+#include <boost/filesystem.hpp>
+
+namespace fs = boost::filesystem;
 
 
 namespace Slic3r { namespace GUI {