[Epic]: migration of the new store module

[cool-develope]

Since we are using a new node key format (cosmos/iavl#676), we need to migrate the original iavl store to the new version.
The migration will proceed in two main stages. Let's assume the current store keeps fromHeight to toHeight of blocks.

• it will create the snapshot for the fromHeight through exporting in the original version and then import that snapshot into the new version.
• it will iterate ChangeSets for fromHeight+1 to toHeight using TraverseStateChanges in the original version and then save those ChangeSets using SaveChangeSet in the new version

ref: #15568, cosmos/iavl#675, cosmos/iavl#676

[cool-develope]

@tac0turtle ☝️

[tac0turtle]

will this all be handled from within IAVL? i think having the store pacakage handle the transition may lead to unforeseen complexity

[tac0turtle]

closed via #15568