For encrypt and decrypt lowering LWE to Polynomial, add support for encryption schemes besides BGV

[Lawrence Lim]

Our encryption and decryption when lowering LWE to Polynomial (in LWEToPolynomial.cpp) currently only supports BGV and there is still work to do to add support for CKKS, TFHE, and BFV. See #874 for the PR adding the lowering for encrypt and #779 for the PR adding the lowering for decrypt.

See also: #834.