Add VerifyChannelUpgradeError and VerifyChannelUpgradeErrorAbsence methods to 03-connection

[damiannolan]

Summary

The UpgradeErrorPath MUST have an associated verification membership and non-membership function so that a counterparty may verify that chain has stored an empty or non-empty error in the UpgradeErrorPath.

Using the existing state verification keeper functions in 03-connection for reference:

• VerifyChannelUpgradeError

• Retrieve the ClientState and associated store using the provided connectionEnd

  • An error should be returned if the ClientState cannot be found
  • An error should be returned if the ClientState is inactive

• Construct the MerklePath using the UpgradeErrorPath defined in 24-host

• Invoke VerifyMembership using the associated ClientState

func (k Keeper) VerifyChannelUpgradeError(
	ctx sdk.Context,
	connection exported.ConnectionI,
	height exported.Height,
	proof []byte,
	portID,
	channelID string,
        errorReceipt channeltypes.ErrorReceipt,
) error {
        return nil
}

---

• VerifyChannelUpgradeErrorAbsence

• Retrieve the ClientState and associated store using the provided connectionEnd

  • An error should be returned if the ClientState cannot be found
  • An error should be returned if the ClientState is inactive

• Construct the MerklePath using the UpgradeErrorPath defined in 24-host

• Invoke VerifyNonMembership using the associated ClientState

func (k Keeper) VerifyChannelUpgradeErrorAbsence(
	ctx sdk.Context,
	connection exported.ConnectionI,
	height exported.Height,
	proof []byte,
	portID,
	channelID string,
) error {
        return nil
}

Ref: https://github.com/cosmos/ibc/blob/master/spec/core/ics-004-channel-and-packet-semantics/UPGRADES.md#UpgradeError-Path

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Note the ClientState interface will contain a generic VerifyMembership method following the completion of:

• Add generic state verification functions to ClientState interface #1145

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For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged/assigned

[damiannolan]

I'm going to start putting tests in place for this issue until we VerifyMembership and VerifyNonMembership merged into the feat branch