feat(x/tx): implement SIGN_MODE_DIRECT_AUX handler

[kocubinski]

Description

Closes: #15169

This patch ports logic from x/auth/tx/direct_aux.go and x/auth/tx/direct_aux_test.go to this new API.

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[aaronc]

We should be able to pass the file resolver into these options. I think it just requires us changing the options struct to use the correct interface

[kocubinski]

Can you explain a bit more what you mean?

Here a user could set GetSignersContext.protoFiles to whatever they want to by constructing it themselves and passing it in.

Edit: Are you saying that GetSignersContext ought to type protoFiles as the interface protodesc.Resolver instead of protoregistry.Files ?

[aaronc]

Yeah, but if they pass in FileResolver but not GetSignersContext, the GetSignersContext should be constructed with that FileResolver. Generally FileResolver and TypeResolver should be propagated to any component that needs them because the probuf types in a scope should all be the same.

[kocubinski]

Ok this will be a refactor to GetSignersContext then, right?

[aaronc]

Yes a bit. We probably need a new interface that extends FileResolver