ADR-040 Implementation: Review and refactor MultiStore

[i-norden]

Child of #9816

ADR-040 necessitates making many changes at the MultiStore level, so we will take this opportunity to perform a complete refactor of the MultiStore. The old IAVL KVStores are each individually versioned, whereas in the new design versioning is handled internal to the underlying database and so is global for all KVStore buckets in the database.

The main hurdle is ensuring continued compatibility with the IBC standard.

• [x] Update ADR-040 spec: https://github.com/cosmos/cosmos-sdk/pull/9355, https://github.com/cosmos/cosmos-sdk/pull/10191
• [x] v2 MultiStore implementation: https://github.com/cosmos/cosmos-sdk/pull/10430
• [x] New issue to track BaseApp integration: https://github.com/cosmos/cosmos-sdk/issues/10804

Meeting notes:

• https://hackmd.io/UkGso4zcTy2IXIdWYQugIg

Related PR:

• https://github.com/cosmos/cosmos-sdk/pull/9355

Related issue:

• https://github.com/cosmos/cosmos-sdk/issues/9818

Related discussions:

• https://github.com/cosmos/ibc-go/discussions/256
• https://github.com/cosmos/cosmos-sdk/discussions/9331
• https://github.com/cosmos/cosmos-sdk/discussions/8297

For Admin Use

• [ ] Not duplicate issue
• [ ] Appropriate labels applied
• [ ] Appropriate contributors tagged
• [ ] Contributor assigned/self-assigned

[i-norden]

Closing as the remaining sub-task is tracked in this issue: https://github.com/cosmos/cosmos-sdk/issues/10804