Gelu10 (#15676)
* Add GeLU10 (clipped version of GeLU) to transformers to improve quantization performances.
* Add unittests.
* Import tensorflow after `is_tf_available` check.
* Fix tensorflow wrong function `tf.tensor` to `tf.constant`
* style.
* use `tf.math.max`
* Fix tf tests.
* style.
* style style style style style style
* style style style style style style
* Address @sgugger comments.
* Fix wrong operator for raising ValueError for ClippedGELUActivation.