[split_special_tokens] Add support for split_special_tokens argument to encode (#25081)

* draft changes

* update and add tests

* styling for no

* move test

* path to usable model

* update test

* small update

* update bertbased tokenizers

* don'tuse kwargs for _tokenize

* don'tuse kwargs for _tokenize

* fix copies

* update

* update test for special tokenizers

* fixup

* skip two tests

* remove pdb breakpiont()

* wowo

* rewrite custom tests

* nits

* revert chang in target keys

* fix markup lm

* update documentation of the argument

tests/models/layoutlmv2/test_tokenization_layoutlmv2.py

@@ -384,6 +384,10 @@ class LayoutLMv2TokenizationTest(TokenizerTesterMixin, unittest.TestCase):
     def test_right_and_left_truncation(self):
         pass
 
+    @unittest.skip("Not implemented")
+    def test_split_special_tokens(self):
+        pass
+
     def test_encode_plus_with_padding(self):
         tokenizers = self.get_tokenizers(do_lower_case=False)
         for tokenizer in tokenizers: