Remove dependency on ibc-go from capability module

[damiannolan]

Summary

Currently the capability module maintained under modules/capability depends on ibc-go in order to make use of simapp under testing/simapp.

The capability module does NOT make use of any ibctesting features such as:

• TestChain
• Path
• Endpoint
• Coordinator

The capability module uses the ibc-go dependency in testing ONLY. It uses simapp for instantiating a new test app and making use of baseapp as well as key functionality such as GetKey and GetMemKey within test funcs.

Problem Definition

While diving into #3978 I noticed how problematic this becomes when performing dependency updates, particularly with the sdk.
The PR in progress currently relies on a fork containing sdk v0.50 code in ibc-go in order to service the capability module's testing.

Without the fork we run into compiler errors, for example, such as store types being now imported from cosmossdk.io/store rather than the previously used github.com/cosmos/cosmos-sdk/store/types.

This becomes a real headache when trying to iterate quickly and upgrade go modules in isolation.

Proposal

Add a lightweight testing app to modules/capability in order to provide testing functionality.
It should be desirable to keep the testing app as barebones as possible - even importing and bootstrapping the app with baseapp and x/capability if at all possible.

This will alleviate issues with the Eden upgrade in progress and allow us to iterate quickly and in isolation without having to rely on ibc-go or any other simulation app as a dependency.

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For Admin Use

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

[damiannolan]

See #4057 (comment)

I've opened #4068 to address the upgrade and remove the ibc-go dependency, while not adding any simapp to the capability module.