Merge pull request #25986 from asmorkalov:as/js_for_contrib

Split Javascript white-list to support contrib modules #25986

Single whitelist converted to several per-module json files. They are concatenated automatically and can be overriden by user config.

Related to https://github.com/opencv/opencv/pull/25656

### 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
- [ ] 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/video/misc/js/gen_dict.json

@@ -0,0 +1,17 @@
+{
+    "whitelist":
+    {
+        "": [
+            "CamShift",
+            "calcOpticalFlowFarneback",
+            "calcOpticalFlowPyrLK",
+            "createBackgroundSubtractorMOG2",
+            "findTransformECC",
+            "meanShift"
+        ],
+        "BackgroundSubtractorMOG2": ["BackgroundSubtractorMOG2", "apply"],
+        "BackgroundSubtractor": ["apply", "getBackgroundImage"],
+        "TrackerMIL": ["create"],
+        "TrackerMIL_Params": []
+    }
+}