Migrate ApprovalController to BaseControllerV2

[rekmarks]

This PR migrates the ApprovalController to BaseControllerV2. Its functionality is exactly the same as before, with the exception of some name changes for clarity, and the addition of controller messenger actions.

The method resolve has been renamed to accept, which is a breaking change.

[Gudahtt]

The two inaccurate comments should be cleaned up, but everything looks great otherwise!

[Gudahtt]

I think I lean more towards unified signatures here as well 🤔 The separate descriptions are kinda nice, but we could explain both origin and type in the unified signature. This seems like it would be more burdensome to maintain.

But I'd be OK with us trying this anyway if you'd prefer. I've never tried it before. Not a big deal 🤷

[rekmarks]

It may make it somewhat more burdensome to maintain, but I think it does make the method easier to use. We can always get rid of the signatures in the future, if it's too much. Since the implementation is very permissive with its parameters, it shouldn't be breaking.

[rekmarks]

I added events to be emitted when requests are approved or reject in the latest commit (4d5be86 at the time of writing). I'm not certain that we'll actually use them in practice, so I'm down to move them to a separate PR, or whatever we may desire.

Meh, I decided against it. The accept and reject signatures allow resolving any value and error, respectively, so there shouldn't be any contextual information that can't be passed to whoever is waiting on the approval promise resolution. That "whoever" can then emit more specific events.

[Gudahtt]

LGTM!