Sarkars/bypass ngcore (#2659)

* Save and return backend handle

* Removing some unnecessary functions

* Implement get_backend_node

* Add documentation

* Applied style

* Change name of function

* Returning op instead of node

* Change documentation

* Added more detailed comments

* Change op to node

src/ngraph/runtime/backend.cpp

@@ -29,6 +29,12 @@ runtime::Backend::~Backend()
 {
 }
 
+std::shared_ptr<ngraph::Node> runtime::Backend::get_backend_op(const std::string& op_name, ...)
+{
+    std::shared_ptr<ngraph::Node> dummy_node(nullptr);
+    return dummy_node;
+}
+
 unique_ptr<runtime::Backend> runtime::Backend::create(const string& type)
 {
     return BackendManager::create_backend(type);

src/ngraph/runtime/backend.hpp

@@ -109,4 +109,12 @@ public:
     virtual bool is_supported_property(const Property prop) const;
 
     virtual void remove_compiled_function(std::shared_ptr<Executable> exec);
+
+    // \brief Return a backend specific op (that is not a core ngraph op).
+    //     The string op_name is the requested op, which a backend may or may not implement.
+    //     If unsupported, nullptr is returned, else a backend op is returned.
+    //     The variadic input is used to pass inputs that the op constructor might take
+    // \param op_name is the name of the backend specific op
+    // \returns a shared pointer to the op if found, else nullptr
+    virtual std::shared_ptr<ngraph::Node> get_backend_op(const std::string& op_name, ...);
 };