Add mish fusion transformation (#1399)

* Add mish fusion transformation

* Add mish op to python api

ngraph/python/src/ngraph/__init__.py

@@ -95,6 +95,7 @@ from ngraph.opset4 import matmul
 from ngraph.opset4 import max_pool
 from ngraph.opset4 import maximum
 from ngraph.opset4 import minimum
+from ngraph.opset4 import mish
 from ngraph.opset4 import mod
 from ngraph.opset4 import multiply
 from ngraph.opset4 import mvn

ngraph/python/src/ngraph/opset4/__init__.py

@@ -84,6 +84,7 @@ from ngraph.opset1.ops import matmul
 from ngraph.opset1.ops import max_pool
 from ngraph.opset1.ops import maximum
 from ngraph.opset1.ops import minimum
+from ngraph.opset4.ops import mish
 from ngraph.opset1.ops import mod
 from ngraph.opset1.ops import multiply
 from ngraph.opset2.ops import mvn

ngraph/python/src/ngraph/opset4/ops.py

@@ -137,3 +137,13 @@ def non_max_suppression(
     }
 
     return _get_node_factory_opset4().create("NonMaxSuppression", inputs, attributes)
+
+
+@nameable_op
+def mish(data: NodeInput, name: Optional[str] = None,) -> Node:
+    """Return a node which performs Mish.
+
+    :param data: Tensor with input data floating point type.
+    :return: The new node which performs Mish
+    """
+    return _get_node_factory_opset4().create("Mish", as_nodes(data), {})