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/HMS.cpp

@@ -25,6 +25,8 @@
 #include <mutex>
 #include <ctime>
 
+namespace fs = boost::filesystem;
+
 static const char* HMS_PATH = "hms";
 static const char* HMS_LOCAL_IMG_PATH = "hms/local_image";