Clean up pagination and other code in post_view.rs

[dessalines]

Requirements

• Is this a feature request? For questions or discussions use https://lemmy.ml/c/lemmy_support
• Did you check to see if this issue already exists?
• Is this only a feature request? Do not put multiple feature requests in one issue.
• Is this a backend issue? Use the lemmy-ui repo for UI / frontend issues.
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Is your proposal related to a problem?

In reworking / abstracting a lot of the pagination code, I tried to add this for post_view, but failed, as its a complete mess at the moment.

• PostQuery calls itself and passes in itself to prefetch some bounds.
• The pagination cursor does two separate fetches to two tables before even querying the list
• It has some hard to follow logic for pagination, that is now unlike the others.
• It uses an overly-complicated PaginationData struct. Ideally it should only need Post or PostActions
• It uses search_term, which is now deprecated
• It uses liked_only / disliked_only, which should be separated into its own endpoint, Order liked_only and disliked_only by vote date #4499
• The code for backward pagination is only half done Backwards pagination for posts #4606

cc @dullbananas @phiresky

Describe the solution you'd like.

See above

Describe alternatives you've considered.

NA

Additional context

Dependent on #5424