Respect __array__ and __array_interface__ for string types

__array__ fixes use-cases like:

  import tensorflow as tf
  import pandas as pd
  series = pd.Series(['a','b','c'])
  tf.constant(series)
  df = pd.DataFrame({'a':[1,2,3],'b':['a','b','c']})
  tf.data.Dataset.from_tensor_slices(dict(df))

PiperOrigin-RevId: 172372593