Merge pull request #24773 from tailsu:sd/pathlike

python: accept path-like objects wherever file names are expected #24773

Merry Christmas, all 🎄

Implements #15731

Support is enabled for all arguments named `filename` or `filepath` (case-insensitive), or annotated with `CV_WRAP_FILE_PATH`.

Support is based on `PyOS_FSPath`, which is available in Python 3.6+. When running on older Python versions the arguments must have a `str` value as before.

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/python/src2/cv2_convert.cpp

@@ -701,6 +701,18 @@ bool pyopencv_to(PyObject* obj, String &value, const ArgInfo& info)
         return true;
     }
     std::string str;
+
+#if ((PY_VERSION_HEX >= 0x03060000) && !defined(Py_LIMITED_API)) || (Py_LIMITED_API >= 0x03060000)
+    if (info.pathlike)
+    {
+        obj = PyOS_FSPath(obj);
+        if (PyErr_Occurred())
+        {
+            failmsg("Expected '%s' to be a str or path-like object", info.name);
+            return false;
+        }
+    }
+#endif
     if (getUnicodeString(obj, str))
     {
         value = str;