Merge pull request #24350 from dkurt:py_return_non_utf8_string

Encode QR code data to UTF-8 #24350

### Pull Request Readiness Checklist

**Merge with extra**: https://github.com/opencv/opencv_extra/pull/1105

resolves https://github.com/opencv/opencv/issues/23728

This is first PR in a series. Here we just return a raw Unicode. Later I will try expand QR codes decoding methods to use ECI assignment number and return a string with proper encoding, not only UTF-8 or raw unicode.

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
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/objdetect/test/test_qrcode.cpp

@@ -637,4 +637,25 @@ TEST_P(Objdetect_QRCode_detectAndDecodeMulti, decode_9_qrcodes_version7)
 
 #endif // UPDATE_QRCODE_TEST_DATA
 
+TEST(Objdetect_QRCode_detectAndDecode, utf8_output)
+{
+#ifndef HAVE_QUIRC
+    throw SkipTestException("Quirc is required for decoding");
+#else
+    const std::string name_current_image = "umlaut.png";
+    const std::string root = "qrcode/";
+
+    std::string image_path = findDataFile(root + name_current_image);
+    Mat src = imread(image_path);
+    ASSERT_FALSE(src.empty()) << "Can't read image: " << image_path;
+
+    QRCodeDetector qrcode;
+    std::vector<Point> corners;
+    Mat straight;
+    std::string decoded_info = qrcode.detectAndDecode(src, corners, straight);
+    EXPECT_FALSE(decoded_info.empty());
+    EXPECT_NE(decoded_info.find("M\xc3\xbcllheimstrasse"), std::string::npos);
+#endif // HAVE_QUIRC
+}
+
 }} // namespace