[T5, MT5, UMT5] Add [T5, MT5, UMT5]ForSequenceClassification (#24726)

* Initial addition of t5forsequenceclassification

* Adding imports and adding tests

* Formatting

* Running make fix-copies

* Adding mt5forseq

* Formatting

* run make fix-copies

* Adding to docs

* Add model_parallel

* Fix bug

* Fix

* Remove TODO

* Fixing tests for T5ForSequenceClassification

* Undo changes to dependency_versions_table.py

* Change classification head to work with T5Config directly

* Change seq length to let tests pass

* PR comments for formatting

* Formatting

* Initial addition of UMT5ForSequenceClassification

* Adding to inits and formatting

* run make fix-copies

* Add doc for UMT5ForSeqClass

* Update UMT5 config

* Fix docs

* Skip torch fx test for SequenceClassification

* Formatting

* Add skip to UMT5 tests as well

* Fix umt5 tests

* Running make fix-copies

* PR comments

* Fix for change to sentence_representation

* Rename seq_len to hidden_size since that's what it is

* Use base_model to follow format of the rest of the library

* Update docs

* Extract the decoder_input_ids changes and make one liner

* Make one-liner

docs/source/en/model_doc/t5.md

@@ -401,6 +401,11 @@ A list of official Hugging Face and community (indicated by 🌎) resources to h
 [[autodoc]] T5EncoderModel
     - forward
 
+## T5ForSequenceClassification
+
+[[autodoc]] T5ForSequenceClassification
+    - forward
+
 ## T5ForQuestionAnswering
 
 [[autodoc]] T5ForQuestionAnswering