Move away from Tx interfaces (sdk.Tx, sdk.FeeTx...)

[amaury1093]

Problem

We used to introduce these interfaces to support both proto Txs (*tx.Tx) and amino (StdTx...)

In the middlewares, we are currently hardcoding the sdk.Tx interface, which introduces a lot of type casting in the implementation.

Ideas

Deprecate:

https://github.com/cosmos/cosmos-sdk/blob/994219a4d2f467a0bd628d60d8670c1102edbe88/types/tx_msg.go#L38-L69

and slowly remove its usage from code.

• Remove StdTx
• Focus only on the protobuf tx path
• Remove the sdk.{TxWithMemo, FeeTx, TxWithTimeoutHeight...} interfaces and use the *tx.Tx proto-generated Tx struct instead
• Replace the tx middleware interface to use tx.Tx

  
  // TxHandler defines the baseapp's CheckTx, DeliverTx and Simulate respective
  // handlers. It is designed as a middleware stack.
  type Handler interface {

• DeliverTx(ctx context.Context, tx sdk.Tx, req abci.RequestDeliverTx) (abci.ResponseDeliverTx, error)
• DeliverTx(ctx context.Context, tx *tx.Tx, req abci.RequestDeliverTx) (abci.ResponseDeliverTx, error) }

Proposal

Step 1: Change the middleware interface to use concrete Tx.

We need to do the following changes:

1. Make the wrapper public. Probably find a better name, but we can use Wrapper for now.

2. Change the tx.Handler interface

- CheckTx(ctx context.Context, tx sdk.Tx, req abci.RequestCheckTx) (abci.ResponseCheckTx, error)
+ CheckTx(ctx context.Context, tx tx.Wrapper, req abci.RequestCheckTx) (abci.ResponseCheckTx, error)

Make sure there's no dep cycles.

3. In the middleware implementations, remove all type casting.

Notes

The last place where amino StdTx were used by default was in legacy API, which was removed in #9594 .

[amaury1093]

Let's wait for this. It's too big a refactor, and not worth it for 0.45. ref: https://github.com/cosmos/cosmos-sdk/pull/10480#issuecomment-963205811