[Refactor]: Support batch inference traceable by ONNX in SSD, YOLOv3, FSAF, RetinaNet, and FCOS (#4699)

* Support batch infer in RetinaNet

* Suport batch multiclass_nms

* Revert multiclass_nms

* Fix api deprecated warning

* do not repeat anchors

* Move img_shapes

* Update Yolov3

* Support FCOS

* Support RPN

* Fix RPN topk_inds error

* make batch exportable to onnx for yolohead

* make fcos_head exportable to onnx with batch dim

* Support ATSS

* Support CornerNet and centripetalNet

* Update RetinaNet and delta_xywh

* Remove ugly code

* Remove ugly code of FCOS

* Remove ugly code of ATSS/YOLOV3

* Support RPN and revert bbox_head

* expand anchors to batch and remove BG class when use deploy_nms_pre

* Update

* Use dim=-1 instead of dim=2

* Rename anchor_head method

* Keep the original format output when nms is not use

* Rename method and unified code style

* Fix paa_head and unittest

* Fix FASF onnx export error

* Fix error

* fix single stage img_shapes for onnx

* move conf_thr

* fix rpn_head for onnx

* Add distance2bbox unittest

* Remove TODO

* Fix RPN

* Update docstrs

Co-authored-by: maningsheng <maningsheng@sensetime.com>