GetStateInfo and MustGetStateInfo can be more efficient

[ThanhNhann]

We can update RollappKeeper.GetStateInfo(ctx sdk.Context, rollappId string, index uint64) to RollappKeeper.GetStateInfo(ctx sdk.Context, stateInfoIndex rtypes.StateInfoIndex) because stateInfoIndex includes rollappId and index

type StateInfoIndex struct {
	// rollappId is the rollapp that the sequencer belongs to and asking to update
	// it used to identify the what rollapp a StateInfo belongs
	// The rollappId follows the same standard as cosmos chain_id
	RollappId string `protobuf:"bytes,1,opt,name=rollappId,proto3" json:"rollappId,omitempty"`
	// index is a sequential increasing number, updating on each
	// state update used for indexing to a specific state info, the first index is 1
	Index uint64 `protobuf:"varint,2,opt,name=index,proto3" json:"index,omitempty"`
}