docstr: `Dictionary` can be saved as textfile. 
code: def test_saveAsText(self):
      """`Dictionary` can be saved as textfile."""
      tmpf = get_tmpfile("save_dict_test.txt")
      small_text = [
          ["prvé", "slovo"],
          ["slovo", "druhé"],
          ["druhé", "slovo"],
      ]
  
      d = Dictionary(small_text)
  
      d.save_as_text(tmpf)
      with codecs.open(tmpf, "r", encoding="utf-8") as file:
          serialized_lines = file.readlines()
          self.assertEqual(serialized_lines[0], "3\n")
          self.assertEqual(len(serialized_lines), 4)
          # We do not know, which word will have which index
          self.assertEqual(serialized_lines[1][1:], "\tdruhé\t2\n")
          self.assertEqual(serialized_lines[2][1:], "\tprvé\t1\n")
          self.assertEqual(serialized_lines[3][1:], "\tslovo\t3\n")
  
      d.save_as_text(tmpf, sort_by_word=False)
      with codecs.open(tmpf, "r", encoding="utf-8") as file:
          serialized_lines = file.readlines()
          self.assertEqual(serialized_lines[0], "3\n")
          self.assertEqual(len(serialized_lines), 4)
          self.assertEqual(serialized_lines[1][1:], "\tslovo\t3\n")
          self.assertEqual(serialized_lines[2][1:], "\tdruhé\t2\n")
          self.assertEqual(serialized_lines[3][1:], "\tprvé\t1\n")
  
imports: from collections.abc import Mapping
  from itertools import chain
  import logging
  import unittest
  import codecs
  import os
  import os.path
  import scipy
  import gensim
  from gensim.corpora import Dictionary
  from gensim.utils import to_utf8
  from gensim.test.utils import get_tmpfile, common_texts
label_desc: Use image node_id 16 for calling the TestDictionary obj's underlying member method code with example usage: obj.test_saveAsText() without return types