Better TF docstring types (#23477)

* Rework TF type hints to use | None instead of Optional[] for tf.Tensor

* Rework TF type hints to use | None instead of Optional[] for tf.Tensor

* Don't forget the imports

* Add the imports to tests too

* make fixup

* Refactor tests that depended on get_type_hints

* Better test refactor

* Fix an old hidden bug in the test_keras_fit input creation code

* Fix for the Deit tests

tests/models/mobilevit/test_modeling_tf_mobilevit.py

@@ -15,6 +15,8 @@
 """ Testing suite for the TensorFlow MobileViT model. """
 
 
+from __future__ import annotations
+
 import inspect
 import unittest