Support Higher Dimensional Ciphertexts and Keys for TFHE when Lowering RLWE to Polynomial

Currently, our lowering for RLWE to Polynomial does not handle TFHE. Other schemes, like BGV have ciphertexts composed of 2 polynomials and a secret key composed of 1 polynomial; however, TFHE supports higher dimensional ciphertexts and Keys. See [this link](https://www.zama.ai/post/tfhe-deep-dive-part-1) for details on TFHE encryption and decryption. Also, see [LWEToPolynomial.cpp](https://github.com/google/heir/blob/main/lib/Conversion/LWEToPolynomial/LWEToPolynomial.cpp) for where to adjust code.

See also #882.