Fix 29807 sinusoidal positional encodings in Flaubert, Informer and XLM (#29904)
* Fix sinusoidal_embeddings in FlaubertModel
* Fix for Informer
* Fix for XLM
* Move sinusoidal emb for XLM
* Move sinusoidal emb for Flaubert
* Small cleanup
* Add comments on tests code copied from
* Add with Distilbert->