Load checkpoint in cpp (#12352)
* Load checkpoint in cpp
* removed unused imports
* throw error on invalid name and change function name
* inplace model assignment, change name and other comments resolved
* name change on import
* Addded unit test, resolved comments
* remove unused imports
* resolved comments
* refactoring too reduce memoory allocation
* resolved extra comments
* changed files hierarchy an force added onnx moodel
* solved order of function argument
* used gtest macros on test cases
Co-authored-by: Adam Louly <adamlouly@microsoft.com@orttrainingdev7.d32nl1ml4oruzj4qz3bqlggovf.px.internal.cloudapp.net>
