message: Add epoch funcs for BigQuery
diff: @@ -2421,6 +2421,14 @@ class BQEngineSpec(BaseEngineSpec):
  return [sqla.literal_column(c.get('name')).label(c.get('name').replace('.', '__'))
  for c in cols]
  + @classmethod
  + def epoch_to_dttm(cls):
  + return 'TIMESTAMP_SECONDS({col})'
  +
  + @classmethod
  + def epoch_ms_to_dttm(cls):
  + return 'TIMESTAMP_MILLIS({col})'
  +
  class ImpalaEngineSpec(BaseEngineSpec):
  """Engine spec for Cloudera's Impala"""
  