Change the way Model Optimizer loads frontends (#7330)

* Adds two switches `use_new_frontend` and `use_legacy_frontend` to override defaults.
* Rename ONNX frontend from `onnx_experimental` to `onnx`

runtime/bindings/python/src/compatibility/pyngraph/frontend/frontend.cpp

@@ -136,4 +136,8 @@ void regclass_pyngraph_FrontEnd(py::module m) {
                 get_name : str
                     Current frontend name. Empty string if not implemented.
             )");
+
+    fem.def("__repr__", [](const ngraph::frontend::FrontEnd& self) -> std::string {
+        return "<FrontEnd '" + self.get_name() + "'>";
+    });
 }

runtime/bindings/python/src/compatibility/pyngraph/frontend/frontend_manager.cpp

@@ -78,6 +78,10 @@ void regclass_pyngraph_FrontEndManager(py::module m) {
                 load_by_model : FrontEnd
                     Frontend interface for further loading of models. 'None' if no suitable frontend is found
             )");
+
+    fem.def("__repr__", [](const ngraph::frontend::FrontEndManager& self) -> std::string {
+        return "<FrontEndManager>";
+    });
 }
 
 void regclass_pyngraph_GeneralFailureFrontEnd(py::module m) {

runtime/bindings/python/tests/test_frontend/test_frontend_onnx.py

@@ -37,7 +37,7 @@ def run_function(function, *inputs, expected):
 
 fem = FrontEndManager()
 onnx_model_filename = "model.onnx"
-ONNX_FRONTEND_NAME = "onnx_experimental"
+ONNX_FRONTEND_NAME = "onnx"
 
 
 def setup_module():

runtime/bindings/python/tests/test_frontend/test_frontend_onnx_editor.py

@@ -217,7 +217,7 @@ def create_test_onnx_models():
 
 fem = FrontEndManager()
 test_models_names = []
-ONNX_FRONTEND_NAME = "onnx_experimental"
+ONNX_FRONTEND_NAME = "onnx"
 
 
 def setup_module():