Merge pull request #28986 from YangGuanyuhan:ai-aliked-lightglue-pipeline

[GSOC] feat: Add ALIKED feature extractor and LightGlue matcher with DNN integration #28986

## PR Description

### Summary

Integrate ALIKED and LightGlue into OpenCV's `features` module as native`Feature2D` and `DescriptorMatcher` implementations, enabling end-to-end neural feature matching within OpenCV's ecosystem.

---

### What's included

#### New classes

- **`cv::ALIKED`** extends `Feature2D`
  - CNN-based keypoint detection
  - 128-D descriptor extraction via ONNX Runtime

- **`cv::LightGlueMatcher`** extends `DescriptorMatcher`
  - Deep feature matching with spatial context
  - Uses keypoints and image sizes during matching

---

#### API design

- Standard OpenCV patterns:
  - `detectAndCompute()`
  - `match()`
  - `knnMatch()`

- Multiple factory methods:
  - ONNX model path
  - In-memory model buffer
  - Pre-loaded `dnn::Net`

- `Params` structs use `CV_EXPORTS_W_SIMPLE`
  for Python/Java bindings support

- Optional DNN dependency:
  - `HAVE_OPENCV_DNN` guards
  - Stub implementations throw `StsNotImplemented`

---

### Files added

| File | Description |
|------|-------------|
| `src/feature2d_aliked.cpp` | ALIKED implementation |
| `src/matchers_lightglue.cpp` | LightGlueMatcher implementation |
| `src/aliked_context.hpp` | Shared internal context struct |
| `test/test_aliked_lightglue.cpp` | Unit tests (9 test cases) |
| `samples/cpp/example_features_aliked_lightglue.cpp` | Demo application |

---

### Files modified

- `CMakeLists.txt`
  - Add `opencv_dnn` as optional dependency

- `features.hpp`
  - Add ALIKED and LightGlueMatcher declarations

- `precomp.hpp`
  - Add DNN include guard

---

### Usage

```cpp
// Feature extraction
Ptr<ALIKED> aliked =
    ALIKED::create("aliked-n16rot-top1k-640.onnx");

vector<KeyPoint> kpts;
Mat descs;

aliked->detectAndCompute(image, Mat(), kpts, descs);

// Feature matching
Ptr<LightGlueMatcher> lg =
    LightGlueMatcher::create("aliked_lightglue.onnx");

lg->setPairInfo(
    kpts1Mat,
    kpts2Mat,
    img1.size(),
    img2.size()
);

vector<DMatch> matches;
lg->match(descs1, descs2, matches);
````
please refer to samples/cpp/example_features_aliked_lightglue.cpp

---

### Test plan

* Build with `BUILD_LIST=features,dnn`
* Build without DNN:

  * Verify stubs compile
  * Verify `StsNotImplemented` is thrown
* Run:

  * `ctest -R Features2d_ALIKED`
  * `ctest -R Features2d_LightGlueMatcher`
* Run sample application with:

  * Real images
  * Real ONNX models
* Verify Python/Java bindings compile and work

---

### Related

Phase 1 of the
"End-to-End AI Feature Extraction and LightGlue Matching Pipeline"
GSoC project.

Designed to be extensible to:

* XFeat
* SuperPoint
* Other neural feature extractors

### test dependency

Depends on the opencv_extra PR adding ALIKED and LightGlue test models:

- [opencv_extra PR](https://github.com/opencv/opencv_extra/pull/1366)

This PR adds the following ONNX models to `download_models.py`:

- `aliked-n16rot-top1k-640.onnx`
- `aliked_lightglue.onnx`

These models are required for the `features2d` tests in the main OpenCV repository to validate the ALIKED and LightGlue feature extraction and matching pipeline.

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

doc/opencv.bib

@@ -27,6 +27,13 @@
   publisher = {IEEE Computer Society},
   address = {Washington, DC, USA},
 }
+@article{Zhao23,
+  author = {Zhao, Xiaoming and Wu, Xingming and Chen, Weihai and Chen, Peter C. Y. and Xu, Qingsong and Li, Zhengguo},
+  title = {ALIKED: A Lighter Keypoint and Descriptor Extraction Network via Deformable Transformation},
+  journal = {arXiv preprint arXiv:2304.03608},
+  year = {2023},
+  url = {https://arxiv.org/abs/2304.03608},
+}
 @inproceedings{Arandjelovic:2012:TTE:2354409.2355123,
   author = {Arandjelovic, Relja},
   title = {Three Things Everyone Should Know to Improve Object Retrieval},
@@ -759,6 +766,14 @@
   year = {2020},
   url = {https://arxiv.org/abs/1911.08947}
 }
+@inproceedings{Lindenberger23,
+  author = {Lindenberger, Philipp and Sarlin, Paul-Edouard and Pollefeys, Marc},
+  title = {LightGlue: Local Feature Matching at Light Speed},
+  booktitle = {Proceedings of the IEEE/CVF International Conference on Computer Vision (ICCV)},
+  year = {2023},
+  pages = {17627--17638},
+  url = {https://arxiv.org/abs/2306.13643},
+}
 @article{Louhichi07,
   author = {Louhichi, H. and Fournel, T. and Lavest, J. M. and Ben Aissia, H.},
   title = {Self-calibration of Scheimpflug cameras: an easy protocol},