Merge pull request #3827 from asmorkalov:as/gapi_migration

Migrate G-API module from main repo to opencv_contrib #3827

Related to https://github.com/opencv/opencv/pull/26469
Required https://github.com/opencv/opencv/pull/26527
CI: https://github.com/opencv/ci-gha-workflow/pull/201

TODO:
- [x]  Python types generator fix
- [x] CI update

### 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
- [ ] 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/gapi/samples/slides_sobel_gapi.cpp

@@ -0,0 +1,28 @@
+#include <opencv2/videoio.hpp>
+#include <opencv2/highgui.hpp>
+#include <opencv2/gapi.hpp>
+#include <opencv2/gapi/core.hpp>
+#include <opencv2/gapi/imgproc.hpp>
+
+int main(int argc, char *argv[])
+{
+    (void) argc;
+    (void) argv;
+
+    using namespace cv;
+    Mat in_mat = imread("lena.png");
+    Mat out_mat;
+
+    GMat in;
+    GMat gx  = gapi::Sobel(in, CV_32F, 1, 0);
+    GMat gy  = gapi::Sobel(in, CV_32F, 0, 1);
+    GMat mag = gapi::sqrt(  gapi::mul(gx, gx)
+                          + gapi::mul(gy, gy));
+    GMat out = gapi::convertTo(mag, CV_8U);
+
+    GComputation sobel(GIn(in), GOut(out));
+    sobel.apply(in_mat, out_mat);
+
+    imwrite("lena-out.png", out_mat);
+    return 0;
+}