Merge pull request #25387 from fengyuentau:complete-float16_t-renaming

Rename remaining float16_t for future proof #25387

Resolves comment: https://github.com/opencv/opencv/pull/25217#discussion_r1547733187.

`std::float16_t` and `std::bfloat16_t` are introduced since c++23: https://en.cppreference.com/w/cpp/types/floating-point.

### Pull Request Readiness Checklist

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- [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/core/include/opencv2/core/cvdef.h

@@ -900,7 +900,9 @@ inline hfloat hfloatFromBits(ushort w) {
 #endif
 }
 
+#if !defined(__OPENCV_BUILD) && !(defined __STDCPP_FLOAT16_T__) && !(defined __ARM_NEON)
 typedef hfloat float16_t;
+#endif
 
 }
 #endif