Merge pull request #27154 from kinchungwong:logging_callback_simple_c

User-defined logger callback, C-style. #27154

This is a competing PR, an alternative to #27140 

Both functions accept C-style pointer to static functions. Both functions allow restoring the OpenCV built-in implementation by passing in a nullptr.
- replaceWriteLogMessage
- replaceWriteLogMessageEx

This implementation is not compatible with C++ log handler objects.

This implementation has minimal thread safety, in the sense that the function pointer are stored and read atomically. But otherwise, the user-defined static functions must accept calls at all times, even after having been deregistered, because some log calls may have started before deregistering.

### 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
- [ ] The PR is proposed to the proper branch
- [ ] 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/core/include/opencv2/core/utils/logger.hpp

@@ -43,6 +43,44 @@ CV_EXPORTS void writeLogMessage(LogLevel logLevel, const char* message);
 /** Write log message */
 CV_EXPORTS void writeLogMessageEx(LogLevel logLevel, const char* tag, const char* file, int line, const char* func, const char* message);
 
+/**
+ * @brief Function pointer type for writeLogMessage. Used by replaceWriteLogMessage.
+ */
+typedef void (*WriteLogMessageFuncType)(LogLevel, const char*);
+
+/**
+ * @brief Function pointer type for writeLogMessageEx. Used by replaceWriteLogMessageEx.
+ */
+typedef void (*WriteLogMessageExFuncType)(LogLevel, const char*, const char*, int, const char*, const char*);
+
+/**
+ * @brief Replaces the OpenCV writeLogMessage function with a user-defined function.
+ * @note The user-defined function must have the same signature as writeLogMessage.
+ * @note The user-defined function must accept arguments that can be potentially null.
+ * @note The user-defined function must be thread-safe, as OpenCV logging may be called
+ *       from multiple threads.
+ * @note The user-defined function must not perform any action that can trigger
+ *       deadlocks or infinite loop. Many OpenCV functions are not re-entrant.
+ * @note Once replaced, logs will not go through the OpenCV writeLogMessage function.
+ * @note To restore, call this function with a nullptr.
+ */
+CV_EXPORTS void replaceWriteLogMessage(WriteLogMessageFuncType f);
+
+/**
+ * @brief Replaces the OpenCV writeLogMessageEx function with a user-defined function.
+ * @note The user-defined function must have the same signature as writeLogMessage.
+ * @note The user-defined function must accept arguments that can be potentially null.
+ * @note The user-defined function must be thread-safe, as OpenCV logging may be called
+ *       from multiple threads.
+ * @note The user-defined function must not perform any action that can trigger
+ *       deadlocks or infinite loop. Many OpenCV functions are not re-entrant.
+ * @note Once replaced, logs will not go through any of the OpenCV logging functions
+ *       such as writeLogMessage or writeLogMessageEx, until their respective restore
+ *       methods are called.
+ * @note To restore, call this function with a nullptr.
+ */
+CV_EXPORTS void replaceWriteLogMessageEx(WriteLogMessageExFuncType f);
+
 } // namespace
 
 struct LogTagAuto