class_docstr: FCOSHead of ARSL for semi-det(ssod)
  Args:
      fcos_feat (object): Instance of 'FCOSFeat'
      num_classes (int): Number of classes
      fpn_stride (list): The stride of each FPN Layer
      prior_prob (float): Used to set the bias init for the class prediction layer
      fcos_loss (object): Instance of 'FCOSLoss'
      norm_reg_targets (bool): Normalization the regression target if true
      centerness_on_reg (bool): The prediction of centerness on regression or clssification branch
      nms (object): Instance of 'MultiClassNMS'
      trt (bool): Whether to use trt in nms of deploy
code: def get_loss(
      self, fcos_head_outs, tag_labels, tag_bboxes, tag_centerness
  ):
      cls_logits, bboxes_reg, centerness = fcos_head_outs
      return self.fcos_loss(
          cls_logits,
          bboxes_reg,
          centerness,
          tag_labels,
          tag_bboxes,
          tag_centerness,
      )
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import math
  import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddle import ParamAttr
  from paddle.nn.initializer import Normal, Constant
  from ppdet.core.workspace import register
  from ppdet.modeling.layers import ConvNormLayer, MultiClassNMS
label_desc: Use image node_id 3 for calling the FCOSHead_ARSL obj's underlying member method code with example usage: obj.get_loss(fcos_head_outs, tag_labels, tag_bboxes, tag_centerness) and returns: self