[Build] Support build with source code of Paddle2ONNX (#1559)

* Add notes for tensors

* Optimize some apis

* move some warnings

* Support build with Paddle2ONNX

* Add protobuf support

* Fix compile on mac

* add clearn package script

* Add paddle2onnx code

* remove submodule

* Add onnx ocde

* remove softlink

* add onnx code

* fix error

* Add cmake file

* fix patchelf

* update paddle2onnx

* Delete .gitmodules

---------

Co-authored-by: PaddleCI <paddle_ci@example.com>
Co-authored-by: pangyoki <pangyoki@126.com>
Co-authored-by: jiangjiajun <jiangjiajun@baidu.lcom>

third_party/optimizer/tools/mypy-onnx.py

@@ -0,0 +1,25 @@
+#!/usr/bin/env python
+
+# SPDX-License-Identifier: Apache-2.0
+
+
+import subprocess
+import os
+
+
+def main():  # type: () -> None
+    try:
+        root_folder = os.path.realpath(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+        os.chdir(root_folder)
+
+        subprocess.check_call(["mypy", "."])
+        subprocess.check_call(["mypy", "--py2", "."])
+
+        exit(0)
+    except subprocess.CalledProcessError:
+        # Catch this exception because we don't want it to output a backtrace that would clutter the mypy output
+        exit(1)
+
+
+if __name__ == '__main__':
+    main()