Unify copies of GenesisDomainParams across different crates

[teor2345]

Currently, we have multiple copies of the GenesisDomainParams, GenesisDomain, DomainConfigParams and DomainConfig structs across different crates. This also means we have multiple copies of the code that converts between them.

It would make changes easier if we used a single copy of each struct, and split out the common parts into a struct shared by both of them.
If that's not possible, we should document where all the copies are, and why they exist.

For an example where all these structs needed to change, see PR #3350.