cggi: add lower-level CGGI ops

Right now the CGGI dialect contains only boolean gate ops reflecting the high level CGGI gate bootstrapping API. We also want the CGGI dialect to include lower-level operations:

- An intermediate level containing bootstrap ops, such as programmable bootstrap and vanilla bootstrap
- A lower level containing the CGGI-specific implementations of bootstrap, such as external product

Ops that are part of the bootstrap implementation, but are generic—such as LWE modulus switch, LWE key switch, and RLWE->LWE sample extraction—should be in the `lwe` dialect so that they can be reused in other schemes.