Add better transformer support for RoFormer (#680)
* added-support-for-RoFormer-in-BetterTransformers
* add-roformer-in-mapping-dict
* Modified doc and updated test cases
* Corrected bias
* Reformatted using `make style`
* Replaced with BertLayer
* make style
* fix style
Co-authored-by: Felix Marty <9808326+fxmarty@users.noreply.github.com>
