Add test to ensure models can take int64 inputs
Like it says on the tin, this is a test to ensure that our models can take `tf.int64` inputs. I expect this will cause some models to break, in which case this PR will also include patches to ensure that they can take `tf.int64`.
_The documentation is not available anymore as the PR was closed or merged._<|||||>I added small patches to all the models that were failing this test. In all cases, the patch shouldn't break `int32` inputs, since I just cast the dtype of the other operand (which was previously invisibly hardcoded as `tf.int32`) to the dtype of the input tensor.