class_docstr: Creates ShapelyAnnotation (as shapely MultiPolygon).
  Can convert this instance annotation to various formats.
code: def __init__(self, multipolygon: MultiPolygon, slice_bbox=None):
      self.multipolygon = multipolygon
      self.slice_bbox = slice_bbox
  
imports: from typing import List
  from shapely.geometry import CAP_STYLE, JOIN_STYLE, MultiPolygon, Polygon, box
label_desc: Use image node_id 3 to create a new ShapelyAnnotation object  with example: obj = ShapelyAnnotation(multipolygon, slice_bbox)