Header parser explicit constructors support

[VadimLevin]

explicit keyword is removed from the function declaration string.

Resolves: #16988.

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under OpenCV (BSD) License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or other license that is incompatible with OpenCV
• The PR is proposed to proper branch
• There is reference to 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

allow_multiple_commits=1

[alalek]

because simple addition of explicit keyword to batch_replace list in parse_func_decl may result to unwanted consequences

Issue is here because Java bindings tests don't cover VideoCapture constructor.
This is why we need bindings tests. They are minimal tests covering these cases:

• required functionality is wrapped
• parameters/results/errors/exceptions are properly passed to/from C++.

---

Validation of bindings generator changes can be performed by comparing generated code with and without the patch. Changes are reviewed manually.

[VadimLevin]

Constructors with explicit keyword are exported.
Verified with:
javap -classpath ./bin/opencv-430.jar org/opencv/videoio/VideoCapture

Output Before:

Compiled from "VideoCapture.java"
public class org.opencv.videoio.VideoCapture {
  protected final long nativeObj;
  protected org.opencv.videoio.VideoCapture(long);
  public long getNativeObjAddr();
  public static org.opencv.videoio.VideoCapture __fromPtr__(long);
  public org.opencv.videoio.VideoCapture();
  public java.lang.String getBackendName();
  public boolean getExceptionMode();
  public boolean grab();
  public boolean isOpened();
  public boolean open(java.lang.String, int);
  public boolean open(java.lang.String);
  public boolean open(int, int);
  public boolean open(int);
  public boolean read(org.opencv.core.Mat);
  public boolean retrieve(org.opencv.core.Mat, int);
  public boolean retrieve(org.opencv.core.Mat);
  public boolean set(int, double);
  public double get(int);
  public void release();
  public void setExceptionMode(boolean);
  protected void finalize() throws java.lang.Throwable;
}

Output after:

Compiled from "VideoCapture.java"
public class org.opencv.videoio.VideoCapture {
  protected final long nativeObj;
  protected org.opencv.videoio.VideoCapture(long);
  public long getNativeObjAddr();
  public static org.opencv.videoio.VideoCapture __fromPtr__(long);
  public org.opencv.videoio.VideoCapture(java.lang.String, int);
  public org.opencv.videoio.VideoCapture(java.lang.String);
  public org.opencv.videoio.VideoCapture(int, int);
  public org.opencv.videoio.VideoCapture(int);
  public org.opencv.videoio.VideoCapture();
  public java.lang.String getBackendName();
  public boolean getExceptionMode();
  public boolean grab();
  public boolean isOpened();
  public boolean open(java.lang.String, int);
  public boolean open(java.lang.String);
  public boolean open(int, int);
  public boolean open(int);
  public boolean read(org.opencv.core.Mat);
  public boolean retrieve(org.opencv.core.Mat, int);
  public boolean retrieve(org.opencv.core.Mat);
  public boolean set(int, double);
  public double get(int);
  public void release();
  public void setExceptionMode(boolean);
  protected void finalize() throws java.lang.Throwable;
}

[alalek]

Well done! Thank you 👍

Validated through generated code:

• modules/java_bindings_generator (ctors are restored)
• modules/python_bindings_generator (no changes)