Notify user if ENS domain resolution changes

Per [the recommendation of the ENS team](https://docs.ens.domains/dapp-developer-guide/ens-enabling-your-dapp), we should notify users if the resolved address from an ENS name changes.

Prerequisites:
- [x] ENS controller: https://github.com/MetaMask/gaba/pull/151
- [ ] Integrate ENS controller with extension: _PR TBD_
- Beyond simply adding the latest version of `gaba` to the extension, we will replace all ENS name validation/normalization with [the function now exposed by `gaba`](https://github.com/MetaMask/gaba/blob/develop/src/util.ts#L324-L345).

How we warn the user in the UI is an open question.

Start by reviewing the ENS controller prerequisite and the exposed function in gaba's src/util.ts, then examine how the extension currently validates and normalizes ENS names. The issue requires integrating that controller and deciding how to warn users when a resolved address changes, but the UI behavior remains an open question.

Written by the indexing model from the issue text.