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/ConfigWizard.cpp

@@ -83,6 +83,8 @@
 #include "UnsavedChangesDialog.hpp"
 #include "MainFrame.hpp"
 
+namespace fs = boost::filesystem;
+
 #if defined(__linux__) && defined(__WXGTK3__)
 #define wxLinux_gtk3 true
 #else