[contracts] Interface changes

Need to finalize interface changes that we have gotten suggestions on from users.

Things that could be important:

• adding in a receivingAsset that can be the local or adopted asset for that chain
• adding in a way to specify slippage boundaries
• adding in xcallExactOut path -> can do this in an upgrade since only additive if needed
• specifying if you want to use slow or fast liquidity
• add getExecutor() to IConnextHandler.sol to expose the executor via interface. similar to how we have getConnext() in IExecutor.sol

cc @just-a-node – if there’s any other feedback you’ve been getting now is the time to surface it!

[rhlsthrm]

Instead of sending it back through the bridge, they should just be able to retrieve their funds in madAssets and they can send back manually later right? We can wrap this up in a UI but I don’t think this needs to explicitly be part of the protocol.

[just-a-node]

Another request:

• add getExecutor() to IConnextHandler.sol to expose the executor via interface. similar to how we have getConnext() in IExecutor.sol