[Refactor] PostInfo redesign

[Jack-Works]

The current design doesn't support modern Maskbook features well.

It should:

• [ ] Support multiple TypedMessage in a single post (Current way is hacky)
• [ ] Support multiple sources to get TypedMessage (Current way is ugly)
• [ ] Support "knowing" the knowledge of TypedMessage
• [ ] Based on the TypedMessage tree transformation

Other changes:

• [x] Encrypt and decrypt should not call network workers to encode/decode. It should only do TypedMessage => Payload or Payload => TypedMessage conversion
• [ ] For public shared posts, no self-found should not be a problem.

[stale[bot]]

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