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/Widgets/WebView.cpp

@@ -34,6 +34,9 @@
 #include <wx/uri.h>
 #include <wx/filename.h>
 #include <wx/stdpaths.h>
+#include <boost/filesystem.hpp>
+
+namespace fs = boost::filesystem;
 #if defined(__WIN32__) || defined(__WXMAC__)
 #include "wx/private/jsscriptwrapper.h"
 #endif