[Feature]: Add TxIndex / TxBlockPos to transaction.Service

[julienrbrt]

Summary

Possibly add a new method in the transaction.Service.

// Service creates a transaction service.
type Service interface {
	// ExecMode returns the current execution mode.
	ExecMode(ctx context.Context) ExecMode
++    // TxIndex returns the transaction position in a block
++    TxIndex(ctx context.Context) (uint64, error)
}

Problem Definition

No response

Proposed Feature

This method, called func TxIndex(ctx) (uint64, error) or TxBlockPos should return the tx position in a block.
Some consumer (like wasmd) require this and do that manually: https://github.com/CosmWasm/wasmd/blob/02354c6/x/wasm/keeper/ante.go#L25-L55

⚠ This should only be done if it is not ugly to do in baseapp and stf

[tac0turtle]

looking into the design, im not sure this would work in the world of parallelisation. As this is something being explored this api would need to be broken. I would propose keeping the antehandler and not making this part of core.