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/include/opencv2/core.hpp

@@ -150,6 +150,18 @@ It is possible to alternate error processing by using #redirectError().
  */
 CV_EXPORTS CV_NORETURN void error(const Exception& exc);
 
+/*! @brief Flags that allow to midify some functions behavior. Used as set of flags.
+*/
+enum AlgorithmHint {
+    ALGO_DEFAULT = 0, //!< Default algorithm behaviour defined during OpenCV build
+    ALGO_ACCURATE = 1, //!< Use generic portable implementation
+    ALGO_APPROX = 2, //!< Allow alternative approximations to get faster implementation. Behaviour and result depends on a platform
+};
+
+/*! @brief Returns ImplementationHint selected by default, a.k.a. `IMPL_DEFAULT` defined during OpenCV compilation.
+ */
+CV_EXPORTS_W AlgorithmHint getDefaultAlgorithmHint();
+
 enum SortFlags { SORT_EVERY_ROW    = 0, //!< each matrix row is sorted independently
                  SORT_EVERY_COLUMN = 1, //!< each matrix column is sorted
                                         //!< independently; this flag and the previous one are