* Copy inputs to train and test step before modifying them, as this breaks things
* Add XLA tests, fix our loss functions to be XLA-compatible
* make fixup
* Update loss computation test to expect vector of per-sample losses
* Patch loss for TFLED
* Patch loss for TFAlbert
* Add a tf_legacy_loss config flag that enables old loss functions
* Stop using config.get() because it's not a dict
* Skip loss computation test for RAG because its loss is very strange and I'm afraid to rewrite it
* make fixup
* Add XLA-compatible RAG loss
* Fix dtype of loss mask for TFAlbert
* Fix test for XLNet too because it overrides the default one
* make fixup
* Fix config test
* No more depending on GPU NaN behaviour
* Add test, avoid potential zero division
* Fix test item assignment
* Fix loss computation masking test
* make fixup
* Fix dtype bugs
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