Remove Bech32 HRP from IBCv2 PortID format

[chipshort]

As discussed elsewhere before, we want to avoid creating the same problem as #1707 in IBCv2. Since the human readable part (HRP) of the bech32 address can contain characters that are invalid in IBC ports, we can just strip it away in PortIDForContractV2 and add it back in ContractFromPortID2.

Example: The current code produces port IDs like wasm2neutron15ww380rfn7r479tdyxpxa2mg2m8u85vlvdtr5tschh9q8s02gu8s7vr4dc and the new behaviour would produce wasm215ww380rfn7r479tdyxpxa2mg2m8u85vlvdtr5tschh9q8s02gu8s7vr4dc