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/PartSkipDialog.cpp

@@ -62,6 +62,8 @@
 
 #include "DeviceCore/DevManager.h"
 
+namespace fs = boost::filesystem;
+
 namespace Slic3r { namespace GUI {
 
 extern wxString hide_passwd(wxString url, std::vector<wxString> const &passwords);