Core: Import STEP: Cancel button does not cancel (#16499)

* Fix importing .step file when user cancelled import settings dialog
* Refactor object loading python code, fix not using settings when STEP options dialog not shown
* Use custom exception type for user cancelling import instead of `RuntimeError`
* Pull python code out to external file

src/Ext/freecad/CMakeLists.txt

@@ -28,6 +28,7 @@ configure_file(__init__.py.template ${NAMESPACE_INIT})
 
 set(EXT_FILES
     freecad_doc.py
+    module_io.py
     part.py
     partdesign.py
     project_utility.py

src/Ext/freecad/module_io.py

@@ -0,0 +1,13 @@
+def OpenInsertObject(importerModule, objectPath, importMethod, docName = ""):
+    try:
+        importArgs = []
+        importKwargs = {}
+
+        if docName:
+            importArgs.append(docName)
+        if hasattr(importerModule, "importOptions"):
+            importKwargs["options"] = importerModule.importOptions(objectPath)
+
+        getattr(importerModule, importMethod)(objectPath, *importArgs, **importKwargs)
+    except PyExc_FC_AbortIOException:
+        pass