Stop Leaking json Through Headers and Drop Includes Kept Only for the Name (#16221)

* Stop Leaking json Through Headers and Drop Includes Kept Only for the Name

AppConfig.hpp, DeviceManager.hpp and UserManager.hpp carried a global
"using namespace nlohmann;", json_diff.hpp a global "using json =
nlohmann::json;" and PrinterFileSystem.h a global "using nlohmann::json;".
Every file that included one of them, directly or not, could write a
bare json, and 63 did without declaring it.

The last two also made the include checker treat json_diff.hpp and
PrinterFileSystem.h as the headers that provide json, so they were
included from files that use nothing else from them: 57 of the 59
includers of json_diff.hpp never name json_diff.

The five statements are removed. Headers that use the type now spell
nlohmann::json, source files declare their own "using json =
nlohmann::json;", and the includes that only supplied the name are
dropped or replaced by <nlohmann/json.hpp>.

Eight files reached json_diff.hpp only through an include that is now
gone and with it lost that header's "using namespace std;". The std
names they used unqualified are qualified.

* Declare json in OrcaSlicer.cpp on Every Platform

OrcaSlicer.cpp had its "using namespace nlohmann;" and the json include
inside the Linux-only include block, so on Windows and macOS it took
json from AppConfig.hpp's global directive, which is gone. The include
and a "using json = nlohmann::json;" now sit outside the block.

src/slic3r/GUI/3DScene.cpp

@@ -1587,7 +1587,7 @@ bool GLVolumeCollection::check_outside_state(const BuildVolume &build_volume, Mo
                     {
                         std::vector<int> result_filaments;
                         //result_filaments.reserve(conflict_filaments.size());
-                        std::set_intersection (conflict_filament_vector.begin(), conflict_filament_vector.end(), unprintable_filament_vec[index].begin(), unprintable_filament_vec[index].end(), insert_iterator<vector<int>>(result_filaments, result_filaments.begin()));
+                        std::set_intersection (conflict_filament_vector.begin(), conflict_filament_vector.end(), unprintable_filament_vec[index].begin(), unprintable_filament_vec[index].end(), std::insert_iterator<std::vector<int>>(result_filaments, result_filaments.begin()));
                         conflict_filament_vector = result_filaments;
                     }
                 }