Merge pull request #25792 from asmorkalov:as/HAL_fast_GaussianBlur

Added flag to GaussianBlur for faster but not bit-exact implementation #25792

Rationale:
Current implementation of GaussianBlur is almost always bit-exact. It helps to get predictable results according platforms, but prohibits most of approximations and optimization tricks.

The patch converts `borderType` parameter to more generic `flags` and introduces `GAUSS_ALLOW_APPROXIMATIONS` flag to allow not bit-exact implementation. With the flag IPP and generic HAL implementation are called first. The flag naming and location is a subject for discussion.

Replaces https://github.com/opencv/opencv/pull/22073
Possibly related issue: https://github.com/opencv/opencv/issues/24135

### 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
- [ ] 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.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/core/src/system.cpp

@@ -46,6 +46,7 @@
 #include <iostream>
 #include <ostream>
 
+#include <opencv2/core.hpp>
 #include <opencv2/core/utils/configuration.private.hpp>
 #include <opencv2/core/utils/trace.private.hpp>
 
@@ -2888,6 +2889,14 @@ bool restoreFPDenormalsState(const FPDenormalsModeState& state)
 
 }  // namespace details
 
+AlgorithmHint getDefaultAlgorithmHint()
+{
+#ifdef OPENCV_ALGO_HINT_DEFAULT
+    return OPENCV_ALGO_HINT_DEFAULT;
+#else
+    return ALGO_ACCURATE;
+#endif
+};
 
 } // namespace cv