test+i18n: multi-nozzle filament-group goldens and ported strings

Filament-group golden harness (config_a subset) and .3mf multi-nozzle round-trip tests, plus i18n msgids for the ported H2C/A2L strings.

tests/filament_group/CMakeLists.txt

@@ -0,0 +1,23 @@
+get_filename_component(_TEST_NAME ${CMAKE_CURRENT_LIST_DIR} NAME)
+
+set(FG_GOLDEN_DIR ${CMAKE_CURRENT_SOURCE_DIR}/golden)
+file(TO_NATIVE_PATH "${FG_GOLDEN_DIR}" FG_GOLDEN_DIR)
+
+add_executable(${_TEST_NAME}_tests
+    filament_group_regression_main.cpp
+    )
+
+target_link_libraries(${_TEST_NAME}_tests test_common libslic3r nlohmann_json Catch2::Catch2WithMain)
+# ${CMAKE_SOURCE_DIR}/deps_src puts <nlohmann/json.hpp> on the include path the same way the
+# libslic3r translation units resolve it (via the admesh/.. system include); nlohmann_json's own
+# interface dir only exposes <json.hpp>, so the source-tree include is required for the <nlohmann/…>
+# spelling the serializers use.
+target_include_directories(${_TEST_NAME}_tests PRIVATE ${CMAKE_SOURCE_DIR}/src ${CMAKE_SOURCE_DIR}/deps_src)
+target_compile_definitions(${_TEST_NAME}_tests PRIVATE
+    FG_TEST_GOLDEN_DIR=R"\(${FG_GOLDEN_DIR}\)"
+    )
+set_property(TARGET ${_TEST_NAME}_tests PROPERTY FOLDER "tests")
+
+orcaslicer_copy_test_dlls()
+
+orcaslicer_discover_tests(${_TEST_NAME}_tests)