More TF int dtype fixes (#20384)
* Add a test to ensure int dummy inputs are int64
* Move the test into the existing int64 test and update a lot of existing dummies
* Fix remaining dummies
* Fix remaining dummies
* Test for int64 serving sigs as well
* Update core tests to use tf.int64
* Add better messages to the assertions
* Update all serving sigs to int64
* More sneaky hiding tf.int32s
* Add an optional int32 signature in save_pretrained
* make fixup
* Add Amy's suggestions
* Switch all serving sigs back to tf.int32
* Switch all dummies to tf.int32
* Adjust tests to check for tf.int32 instead of tf.int64
* Fix base dummy_inputs dtype
* Start casting to tf.int32 in input_processing
* Change dtype for unpack_inputs test
* Add proper tf.int32 test
* Make the alternate serving signature int64