[assets-controllers] Convert `AssetsContractController` from `BaseControllerV1` to service class utilizing messenger pattern

[MajorLift]

Explanation

As part of the Wallet Framework Team's Q2 2024 OKRs (O3KR1: 100% completion of all core controllers to BaseControllerV2), the AssetsContractController needs to be converted to a V2 controller.

However, because AssetsContractController has an empty state object, it is a non-controller, which should be able to communicate with other controllers using a messagingSystem, but otherwise should not inherit from the BaseControllerV2 class.

References

• Closes https://github.com/MetaMask/core/issues/4072

Changelog

Checklist

• [ ] I've updated the test suite for new or updated code as appropriate
• [ ] I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• [ ] I've highlighted breaking changes using the "BREAKING" category above as appropriate