[docs] Fix BatchEncoding documentation inconsistencies

[samyuktahegde]

What does this PR do?

I found a few inconsistencies in the documentation of BatchEncoding class in the file tokenization_utils_base.py. I have updated them as mentioned in the table below.

Changes

Method / Section	Change
BatchEncoding.__init__()	Corrected the description of n_sequences. It had the description of tensor_type.
tokens(), sequence_ids(), word_ids()	Updated the error message to refer to Python based tokenizers(to maintain consistency within the class). In the earlier version of the message, non-fast tokenizers was mentioned with a contradictory example (XxxTokenizerFast).
token_to_sequence()	Corrected the return description to indicate that the method returns the "input sequence index" containing the token instead of the "word index".
word_to_tokens()	Corrected the parameter reference from batch_or_token_index to batch_or_word_index.
char_to_token()	Corrected the parameter reference from batch_or_token_index to batch_or_char_index, replaced "word" with "character" where appropriate.
word_to_chars()	Corrected the parameter reference from batch_or_token_index to batch_or_word_index, clarified the CharSpan description, corrected the return type.
char_to_word()	Corrected the parameter reference from batch_or_token_index to batch_or_char_index, corrected the return type, and updated the return description to refer to "word" instead of "token".
convert_to_tensors()	Corrected the type of prepend_batch_axis from int to bool.
Multiple methods	Corrected minor grammatical errors

Fixes # (issue)

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[Rocketknight1]

cc @stevhliu

[stevhliu]

thanks!

[github-actions]

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CI recap

Dashboard: View test results in Grafana
Latest run: 30700855549:2
Result: success | Jobs: 16 | Tests: 178,177 | Failures: 0 | Duration: 16h 31m

[HuggingFaceDocBuilderDev]

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