Use one struct per action table in view structs

[dullbananas]

Requirements

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Is your proposal related to a problem?

The current flattened style causes a lot of duplication, which makes it hard to maintain consistency and add new actions to all views.

Describe the solution you'd like.

Create structs such as PostActions and CommunityActions, and use those as fields in view structs, instead of things like like_score being top-level fields.

Describe alternatives you've considered.

Maybe use shared structs that have more than just the actions.

Additional context

No response

[dessalines]

We'd also be able to use diesel_embed if we did that, which would make the selects a lot easier.

The downside would be that the views won't be as clear, especially since a lot of the actions are timestamps. But I'd still be in favor of this as it'd clean up the code a lot.

[Nutomic]

Then we can probably get rid of AssumeNotNull too

[dessalines]

This would be good to include in 1.0.0 then, since it would change all the structs a lot.

After #5407 is merged, we can work on this. I can do it if no one else wants to, and because I did a lot of this already for the combined views. Or @dullbananas if you'd rather do it, lmk.

EDIT: I started working on it.