Fix LED
The hidden states and last states returned by the model were incorrect in both TF and PT, so this hopefully resolves everything.

In addition, this PR disables LayerDrop in the TF model, as its implementation would not work in any model compiled with Keras or `tf.function`

Resolves #13776 
Hmm, it seems like some Torch tests are now failing because they expect the longer padded output length. Not sure whether this is a problem with my fix or with the tests<|||||>@Rocketknight1 - Thanks a lot for the fix! Some generation tests are failing...if you want I can dive into the PR and fix them - lemme know :-)