fix(x/bank): use a more flexible value codec for bank's denom address index.

[testinginprod]

Requires: #16771

After migrating bank to collections, even if it does not show up in code, collections will complain if there's some path that requires reading the index value of bank's denom address index. This never happens because we only care about keys (the denom to address index is represented as a key, with a meaningless value), nonetheless in order to protect forward compatibility we should add a more flexible value codec that accepts values != []byte{} and lazily migrates them to []byte{}.

[likhita-809]

@testinginprod should this be completed as part of bank audit ?

[testinginprod]

@likhita-809 : yes, I will open a PR soon