Merge pull request #25024 from vrabaud:neon

Replace legacy __ARM_NEON__ by __ARM_NEON #25024

Even ACLE 1.1 referes to __ARM_NEON
https://developer.arm.com/documentation/ihi0053/b/?lang=en

### 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
- [x] 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/src/system.cpp

@@ -637,10 +637,10 @@ struct HWFeatures
         }
     #endif
     #elif (defined __APPLE__)
-    #if (defined __ARM_NEON__ || (defined __ARM_NEON && defined __aarch64__))
+    #if defined __ARM_NEON
         have[CV_CPU_NEON] = true;
     #endif
-    #if (defined __ARM_FP  && (((__ARM_FP & 0x2) != 0) && defined __ARM_NEON__))
+    #if (defined __ARM_FP  && (((__ARM_FP & 0x2) != 0) && defined __ARM_NEON))
         have[CV_CPU_FP16] = have[CV_CPU_NEON_FP16] = true;
     #endif
     // system.cpp may be compiled w/o special -march=armv8...+dotprod, -march=armv8...+bf16 etc.,
@@ -659,7 +659,7 @@ struct HWFeatures
         have[CV_CPU_NEON_BF16] = true;
     }
     #elif (defined __clang__)
-    #if (defined __ARM_NEON__ || (defined __ARM_NEON && defined __aarch64__))
+    #if defined __ARM_NEON
         have[CV_CPU_NEON] = true;
         #if (defined __ARM_FP  && ((__ARM_FP & 0x2) != 0))
         have[CV_CPU_FP16] = true;