Fix and improve CTRL doctests (#16573)
* Improve CTRL doctests
* Fix `CTRLForSequenceClassification` flakiness with inconsistent losses
* Remove unused
* Fixup
* Add CTRL to documentation_tests.txt
* Fix control code not being first
* Add output assertions
* Change from sshleifer/tiny-ctrl -> ctrl
* Run `make fixup`
* apply `list` to output logits shape for clarity
* Reduce output loss precision to make assertion more robust
* Add assertion of control code being first
* Fix docstyle
* upper case sentence following control code
* Weird bug fixes
* Add a better generation example
Co-authored-by: Yih-Dar <2521628+ydshieh@users.noreply.github.com>
