Increase test coverage for AesCipher #1232
                
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The tests were generated by a script which is also added for posterity. The script works by running
openssl enc [...](via WSL) to generate the expected encrypted values, and also verifies those values against the .NET BCL implementation as an extra validation before generating the tests.The new tests uncovered a bug in
OfbCipherMode, or rather, that it was an exact duplicate ofCfbCipherMode. The second commit fixes the new failing tests (by following the nice pictures in https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Output_feedback_(OFB)).I would like to help with #865, this should add confidence there.