class_docstr: Maps a feature path to its weight feature.
  
  This map can be created with a "global" weight feature and path-specific
  overrides. For any given FeaturePath, its weight column is the override, if
  specified, or the "global" one.
code: def all_weight_features(self) -> FrozenSet[types.FeatureName]:
      return self._all_weight_features
  
imports: from typing import FrozenSet, Mapping, Optional
  from tensorflow_data_validation import types
label_desc: Use image node_id 3 for calling the ExampleWeightMap obj's underlying member method code with example usage: obj.all_weight_features() and returns: self