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/dev-utils/OrcaSlicer_profile_validator.cpp

@@ -58,6 +58,8 @@
 #include <set>
 #include <string>
 
+namespace fs = boost::filesystem;
+
 using namespace Slic3r;
 namespace po = boost::program_options;