class_docstr: A TF step metric that emits multiple values per step.
  
  The only difference between `TFSTepMetric` and `TFMultiMetricStepMetric` is
  that the latter creates at each step many scalar summaries, one per metric.
code: def __init__(self, name, prefix="Metrics", metric_names=()):
      super(TFMultiMetricStepMetric, self).__init__(name, prefix)
      self._metric_names = metric_names
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import tensorflow
  from tf_agents.utils import common
label_desc: Use image node_id 1 to create a new TFMultiMetricStepMetric object from inherited base classes: TFStepMetric with example: obj = TFMultiMetricStepMetric(name, prefix, metric_names)