The yolov8 object detection and segmentation

1.Android yolov8 detection demo
2.yolov8s-seg.cpp
3.yolov8s-obb.cpp

1.change c2f split to slice

2.for Detection model change class Detect output

3.for Segmentation model change class Detect output and Segment output

https://github.com/nihui/ncnn-android-nanodet
https://github.com/Tencent/ncnn
https://github.com/ultralytics/assets/releases/tag/v0.0.0
https://github.com/facebookresearch/detectron2