ximgproc: move LineSegmentDetector (LSD) from imgproc

[JArmandoAnaya]

As part of the imgproc cleanup in opencv/opencv #25001, this moves the Line
Segment Detector (LineSegmentDetector) from imgproc into ximgproc. LSD is a
self-contained, rarely used detector with no callers elsewhere in the library,
and ximgproc already provides a sibling FastLineDetector, so the extended module
is a more natural home for it.

This is the opencv_contrib side of the change. A companion pull request on the
main repository removes LSD from imgproc, and the two are meant to be merged
together so the detector is never defined in both modules at once. The public
interface is unchanged apart from the namespace, so callers reach the detector
through cv::ximgproc now.

The implementation, the public header (the LineSegmentDetector class, the
createLineSegmentDetector factory and the LineSegmentDetectorModes enum) and
the accuracy test move across unchanged apart from the cv::ximgproc namespace,
so it reads as a straight move. The lsd_lines sample is included as well.

The accuracy test moved with the function and still passes (18 cases across the
NONE / STD / ADV refinement modes and the common draw/compare paths).

• Issue: Clean Imgproc module opencv#25001
• opencv PR: imgproc: move LineSegmentDetector to opencv_contrib opencv#29349

Pull Request Readiness Checklist

• I agree to contribute to the project under Apache 2 License.
• 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