API docs clarification: Document StateSearchMsg replaced message behavior

[magik6k]

State[Wait/Search]Msg methods will return successfully when messages on-chain are gas-repriced. This means that when those methods are used to check if a message has landed on-chain, the caller needs to make sure that the returned MsgLookup.Message is the same message CID they are expecting

The StateGetReceipt method will also accept gas-repriced messages, but it unfortunately doesn't provide a way to check if the message which was executed on-chain was repriced.

[BigLep]

Thoughts concerning the documentation improvement:

1. There is a lot of copy/paste. Is there a way to reduce this?
2. Related, is the content in api-methods.md generated from api_full.go automatically?
3. Should we maybe state that some of our APIs are "replacement message sensitive" (I'm not saying that is the right/best term)? We can then define somewhere what that means and ideally link to that definition where someone can learn more about the specifics. Specifics can cover how this happens, which message replaces another in the tipset, etc.
4. Where can we document guidance for how exchange-like entities should use the API (e.g., consider StateCompute, DON’T use ChainGetBlockMessages and StateGetReceipt -- DO use ChainGetParentMessages, StateSearchMsg, and StateCompute).

• Ideally our "replacement message sensitive" documentation could link to this.

[magik6k]

There is a lot of copy/paste. Is there a way to reduce this?

In v1 API we can consolidate those methods more

Related, is the content in api-methods.md generated from api_full.go automatically?

Yep, that file is generated

Should we maybe state that some of our APIs are "replacement message sensitive"

This is basically what we do in this PR, I don't thing we have more APIs which are replace-sensitive