Add a MockGatewaytest utility contract for developer's unit tests

[lumtis]

When building Universal apps where several contracts must communicate from different chain, it would be useful to offer developers mocked gateway contract so they can run full integration with the Foundry test suite.

The mockedGateway directly call the onCall function when depositAndCall/withdrawAndCall/call function is called.

The contract should also have an interface like setReverting, setAborting to allow simulating the workflow of a reverting or aborting contract.

In this case the functions above would call the onRevert or onAbort functions