Replace swish with silu (#8166)

* Replace swish with silu

* revert nn.silu to nn.swish due to older version

* simplify optimized silu conditional and fix format

* Update activations.py

* Update activations_tf.py

* Update modeling_flax_utils.py

* Update modeling_openai.py

* add swish testcase

* add pytorch swish testcase

* Add more robust python version check

* more formatting fixes

Co-authored-by: TFUsers <TFUsers@gmail.com>

tests/test_activations_tf.py

@@ -12,6 +12,7 @@ if is_tf_available():
 class TestTFActivations(unittest.TestCase):
     def test_get_activation(self):
         get_tf_activation("swish")
+        get_tf_activation("silu")
         get_tf_activation("gelu")
         get_tf_activation("relu")
         get_tf_activation("tanh")