Merge pull request #23724 from dkurt:java_without_ant

Build Java without ANT #23724

### Pull Request Readiness Checklist

Enables a path of building Java bindings without ANT

* Able to build OpenCV JAR and Docs without ANT
  ```
  --   Java:
  --     ant:                         NO
  --     JNI:                         /usr/lib/jvm/default-java/include /usr/lib/jvm/default-java/include/linux /usr/lib/jvm/default-java/include
  --     Java wrappers:               YES
  --     Java tests:                  NO
  ```
* Possible to build OpenCV JAR without ANT but tests still require ANT

**Merge with**: https://github.com/opencv/opencv_contrib/pull/3502

Notes:
- Use `OPENCV_JAVA_IGNORE_ANT=1` to force "Java" flow for building Java bindings
- Java tests still require Apache ANT
- JAR doesn't include `.java` source code files.


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

modules/core/misc/java/src/java/core+Mat.java

@@ -470,6 +470,7 @@ public class Mat {
      * Element-wise multiplication with scale factor
      * @param m operand with with which to perform element-wise multiplication
      * @param scale scale factor
+     * @return reference to a new Mat object
      */
     public Mat mul(Mat m, double scale) {
         return new Mat(n_mul(nativeObj, m.nativeObj, scale));
@@ -478,6 +479,7 @@ public class Mat {
     /**
     * Element-wise multiplication
     * @param m operand with with which to perform element-wise multiplication
+    * @return reference to a new Mat object
     */
     public Mat mul(Mat m) {
         return new Mat(n_mul(nativeObj, m.nativeObj));
@@ -487,6 +489,7 @@ public class Mat {
     * Matrix multiplication
     * @param m operand with with which to perform matrix multiplication
     * @see Core#gemm(Mat, Mat, double, Mat, double, Mat, int)
+    * @return reference to a new Mat object
     */
     public Mat matMul(Mat m) {
         return new Mat(n_matMul(nativeObj, m.nativeObj));