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/Project.cpp

@@ -58,6 +58,8 @@
 #include "MainFrame.hpp"
 #include <slic3r/GUI/Widgets/WebView.hpp>
 
+namespace fs = boost::filesystem;
+
 namespace Slic3r { namespace GUI {
 
 wxDEFINE_EVENT(EVT_PROJECT_RELOAD, wxCommandEvent);