Py transformer coder test (#43976)
Summary:
Fixes #{[37756](https://github.com/pytorch/pytorch/issues/37756)}
Added the missing Transformer coder python test scripts from C++ API test scripts
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43976
Reviewed By: jamesr66a
Differential Revision: D23873250
Pulled By: glaringlee
fbshipit-source-id: cdeae53231e02208463e7629ba2c1f00990150ea
